Free Essays on The Heart

LOST CHILDREN â€Å"As long as any grown-up imagines that he, similar to the guardians and instructors of old, can get thoughtful, summoning his own childhood to comprehend the young before him, he is lost.† Children nowadays, especially youths, will in general feel misconstrued by their folks, and guardians consequently feel that their high school children or little girls are for all intents and purposes hard of hearing. As the security between the parent and kid starts to disintegrate, youngsters start to take asylum in their companions, and their reliance upon companions as opposed to guardians in the end takes cost upon their lives. As youngsters further away from their folks, they start to isolate into a way where returning gets more earnestly constantly. The parent and youngster are delineated in a â€Å"Calvin and Hobbes† animation article where Calvin interprets his mother’s bothering as ‘Blah blah blah†¦Ã¢â‚¬  and makes sure to gesture between his moms delays. In any family, guardians normally advise their youngsters. In spite of the fact that the specific level of bothering and resistance does very among family units, guardians generally right their youngsters in a single manner or the other. In any case, most kids don't take such reprimands well, especially teenagers who typically feel that they have developed past their own folks. Youths generalization their folks as â€Å"old generation† and continually misconstruing them. Young ladies feel as though their folks are over-defensive, while adolescent young men feel that their folks are intrusive about their organizations. Guardians normally set a time limit for their high school girls and remind her to call home on the off chance that she is runn ing late. Despite the fact that her folks stress for her, young ladies feel that their folks are being over-defensive and controlling. Youthful adolescent young ladies feel confined by her father’s curfews and humiliated by the manner in which her folks call her mobile phone each time she stays late for parties. In like manner, high school young men are annoyed by their folks steady addressing over the dinning table,... Free Essays on The Heart Free Essays on The Heart LOST CHILDREN â€Å"As long as any grown-up believes that he, similar to the guardians and educators of old, can get reflective, summoning his own childhood to comprehend the young before him, he is lost.† Children nowadays, especially youths, will in general feel misconstrued by their folks, and guardians consequently feel that their high school children or girls are for all intents and purposes hard of hearing. As the security between the parent and youngster starts to fall apart, kids start to take asylum in their companions, and their reliance upon companions instead of guardians in the long run takes cost upon their lives. As young people further away from their folks, they start to isolate into a way where returning gets more diligently constantly. The parent and youngster are portrayed in a â€Å"Calvin and Hobbes† animation article where Calvin disentangles his mother’s annoying as ‘Blah blah blah†¦Ã¢â‚¬  and makes sure to gesture between his moms delays. In any family, guardians normally advise their youngsters. Despite the fact that the specific level of pestering and resilience does very among families, guardians generally right their youngsters in a single manner or the other. Be that as it may, most kids don't take such reprimands well, especially young people who typically feel that they have developed past their own folks. Young people generalization their folks as â€Å"old generation† and continually misjudging them. Young ladies feel as though their folks are over-defensive, while high school young men feel that their folks are intrusive about their organizations. Guardians normally set a check in time for their high school girls and remind her to call home on the off chance that she is running late. In spite of the fact that her folks stress for her, young ladies feel that their folks are being over-defensive and controlling. Youthful young ladies feel confined by her father’s curfews and humiliated by the manner in which her folks call her mobile phone each time she stays late for parties. In like manner, high school young men are irritated by their folks consistent addressing over the dinning table,...

Stele of Hummurabi essays

Stele of Hummurabi papers Who composed the most punctual composing code law? Hammurabi was the ruler who mainly settled the enormity of Babylon, the world's first city. He is the most punctual known case of a ruler declaring openly to his kin a whole assemblage of laws, orchestrated in methodical gatherings, with the goal that all men may peruse and realize what was expected of them. Hammurabi's most celebrated distinguishing strength is his law code. The code is recorded on a great stele of dark diorite, eight feet high, found at Susa in A.D. 1902. Once in the past it had remained in Babylon, yet the Elamites carted it away when they vanquished Babylon in the twelfth century B.C. It is currently in the Louver Museum in Paris. At the highest point of the stele is a finely formed scene demonstrating Hammurabi remaining before the sun god Shamash (the benefactor of law and equity), who is situated and is giving the laws to Hammurabi. Underneath the scene the laws are recorded in delightful cuneiform characters in fifty-one segments of content. The code is engraved on a tall dark basalt stele that was taken away as goods to Susa in 1157 B.C., along with the Naram-Sin stele. At the top is a help portraying Hammurabi within the sight of the fire should-dered sun god, Shamash. The ruler lifts his hand in regard. The god gives on Hammurabi the position to govern and to implement the laws. The artist delineated Shamash in the recognizable show of consolidated front and side perspectives, however with two significant exemptions. His incredible hat with its four sets of borns is in ceptions. His extraordinary deaddress with its four sets of borns are genuine profile so just four, not every one of the eight, of the horns are obvious. What's more, the craftsman appears to have probably investigated the thought of forehortening a gadget for proposing dept by repersenting a figure or article at a point, as opposed to frontally or in profile. The divine beings whiskers is a progression of askew instead of flat lines, recommending its r evession from the image plane. ... <!

Essay on the Psychological Impact in Ads

Essay on the Psychological Impact in Ads The Psychological Impact in Ads Dec 20, 2018 in Psychology The Psychological Impact in Advertising In advertising, psychology is used in order to provide a service or sell a product. Understanding of the notion that affects human psychology can assist a company to better sell a product or help the customer to comprehend marketing strategies that make them purchase. Persuasion is the shifting of attitudes by presenting information concerning another attitude. The information can be processed peripherally or centrally. If it is processed centrally, attitude change is likely to have performance. There are two routes of the persuasion that may change an individuals belief structure based on cognitive processes that come up at the time of persuasion. The two routes are expressed as the peripheral and central routes. The peripheral route has to do with the fact that individuals cannot exercise effortful and careful analyze every message they come across.

Adolescent Teens And Young Adults Essay - 1550 Words

It is no surprise that the United States has become infatuated with the idea of being fit, thin and healthy. This ideal has become so popular that it has become the new norm all over different media platforms including the ever growing, trendy, and highly accessible social media websites. Instagram, Twitter, Tumblr, and even the surprising Pinterest are just some of the few platforms that glorify the ideal that being thin is better and is the ideal to be wanted, loved, and successful in life. While this ideal may seem harmless to some people, for others it has become a death wish. This ideal has become so saturated in the media people need to take a step back and question how it effecting its targeted audience of adolescent teens and young adults? Asking such a simple question would end up saving many lives and could possibly give psychologist a deeper look on how the media people see everyday effects who we are and how we want to live. This topic is completely multidirectional when it comes to the development of psychology. Not only do people learn these habits from the media but also from the outside culture, their parents, and those closest to them. Everyone will always have a different motivation for doing what they do but it can always be influenced by perspectives around them. For example, one way that the media loves manipulate young adults is to tell them what they should do with their diet in order to improve their body image. According to KathleenShow MoreRelatedDiabetes Mellitus And Its Effects On Children, Teens, Adolescents And Young Adults1581 Words   |  7 PagesIt is reported that nearly 25 million Americans (11.3 percent of adults) have Type II Diabetes now and the number is continuously rising (Fuhrman, 2012, pg.8). This disease is an important and escalating problem worldwide. Generally, Diabetes Mellitus is defined simply as a disease in which the body cannot process and use sugar correctly. As a result, sugar builds in the blood stream causing immediate symptoms of fever, increased thirst and urination, fatigue and if left untreated eventually comaRead MoreThe Purpose Of This Paper Seeks To Analyze The Effects1208 Words   |  5 Pagesdrug problems as it pertains to motivational context. The third and final article seeks to education youn g adults on medical prescription drug use. A parent’s attitudes regarding substance use may help to clarify practical racial/ethnic deviations in prescription drug misuse among teens. The findings add provision to the growing evidence that parents continue to endure a critical part of adolescents decision-making, concerning potentially risky behaviors. This article by Conn and Marks examinesRead MoreThe Absolutely True Diary of a Part-Time Indian Essay1131 Words   |  5 PagesAdolescents experience a developmental journey as they transition from child to adult, and in doing so are faced with many developmental milestones. Physical, cognitive, social and emotional changes are occurring during this tumultuous stage of life, and making sense of one’s self and identity becomes a priority. Sherman Alexie’s The Absolutely True Diary of a Part-Time Indian addresses the challenges of adolescence in an engaging tale, but deals with minority communities and cultures as well. Read MoreEssay on Teen Pregnancy: How to Prevent It781 Words   |  4 PagesTeen Pregnancy Imagine it - Clicking through all the channels on television to find something that would strike any american’s interest. Young looking girls on the television are talking about their lives, and the issues they hold. The show is called Teen Mom. How could such vibrant young ladies have so much responsibility at this age? Why would they take on this role of motherhood when they themselves still depend on the assistance of their own parental figures? 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It’s important to tell teens the turnouts of teen pregnancy for the good and bad parts. There are risks of having sex, teen moms can make a difference for her and the baby, the risk of having HIV and/or any other STD’s, and the effects on theRead MoreBreaking News : Teen Commits Suicide1222 Words   |  5 Pages â€Å"BREAKING NEWS: TEEN COMMITS SUICIDE† is not an unusual headline to read. Time and time again teens are making the choice to end their lives much like Richard Kirchoff’s son, Ryan Kirchoff, who took his life at the young age of 18. Kirchoff’s son was a normal kid who had many friends, a loving family, and dreamt that he would become a successful doctor, but all was taken away after he made the decision to take his life. Ryan had depression and refused to seek help from the people he trusted resultingRead MoreAnalysis Of John Green s Looking For Alaska 1423 Words   |  6 PagesCrippling mental diseases, such as depression and anxiety, have always existed among adults. In recent years, however, the number of adolescents affected by such illnesses has drastically increased. In fact, a 2008 study presented in the Archives of General Psychiatry â€Å"found that nearly half of 19- to 25-year-olds have at least one psychiatric disorder† (Brondou â€Å"Study Shows†¦Ã¢â‚¬ ). The average teenager juggles school, family and social stress as well as transitioning from childhood to adulthood. TheRead MoreTeen Mothers Experiences1027 Words   |  5 Pages This concept is usually thought of by adults that can manage to support a family and acquires a strong partnership with a lifetime companion. Commitment is one of the key concepts to successfully raising a child. However, this exciting news turns into a tragedy for an unexperienced teenager undergoing pregnancy. Teens are unstable for providing an adequate environment for a newborn and lack the skill of being a caretaker. It makes it challenging for teens to incorporate a baby in their life whileRead MoreLegal Age to Drive Should Be Raised to 211443 Words   |  6 PagesTeen drivers are every adult’s nightmare. With the la ck of experience and maturity, both parents and fellow drivers are frightened to share the road with adolescents. Through much research, juveniles as a whole have proven to be incapable of obtaining respectable driving skills. According to â€Å"Rocky Mountain Insurance Information Association,† motor vehicle crashes were the leading cause of death among 13-19 year old males and females in the United States. Culpable for this statistic is the three

Article 20 Arranging a Marriage - 4350 Words

Article 20 Arranging a Marriage in India Serena Nanda John Jay College of Criminal Justice Sister and doctor brother-in-law invite correspondence from North Indian professionals only, for a beautiful, talented, sophisticated, intelligent sister, 5’3, slim, M.A. in textile design, father a senior civil officer. Would prefer immigrant doctors, between 26–29 years. Reply with full details and returnable photo. A well-settled uncle invites matrimonial correspondence from slim, fair, educated South Indian girl, for his nephew, 25 years, smart, M.B.A., green card holder, 5’6. Full particulars with returnable photo appreciated. Matrimonial Advertisements, India Abroad IN INDIA, ALMOST ALL MARRIAGES ARE arranged. Even among the educated†¦show more content†¦Ã¢â‚¬Å"How can you go along with this?† I asked her, in frustration and distress. â€Å"Don’t you care who you marry?† 1 Article 20. Arranging a Marriage in India and did not â€Å"love,† so offended my American ideas of individualism and romanticism, that I persisted with my objections. â€Å"I still can’t imagine it,† I said. â€Å"How can you agree to marry a man you hardly know?† â€Å"But of course he will be known. My parents would never arrange a marriage for me without knowing all about the boy’s family background. Naturally we will not rely only on what the family tells us. We will check the particulars out ourselves. No one will want their daughter to marry into a family that is not good. All these things we will know beforehand.† Impatiently, I responded, â€Å"Sita, I don’t mean know the family, I mean, know the man. How can you marry someone you don’t know personally and don’t love? How can you think of spending your life with someone you may not even like?† â€Å"If he is a good man, why should I not like him?† she said. â€Å"With you people, you know the boy so well before you marry, where will be the fun to get married? There will be no mystery and no romance. Here we have the whole of our married life to get to know and love our husband. â€Å"This way is better, is it not?† HerShow MoreRelatedPersonal Success Plan Essay1139 Words   |  5 Pagesthe article, Training the Person of the therapist in an Academic Setting the authors describes the training model of Person-of-the –therapist (POTT) that was created to enhance the therapist’s skills in therapy. The framework of the model designed to encourage the therapists to examine themselves in four areas to define their strengths and weakness. These skills were limited to only a few institutes in the earlier practices however have expanded throughout the years. While reading this article I tookRead MoreSocio Economic Status Of The United States1443 Words   |  6 Pagesa single parent. There is currently more divor ce in the United States than marriages that last. Which is sad, but with so many choices and opportunities to get divorced or just give up, not to many people the meaning of marriage to heart more of a convenience. 1. http://www.smithsonianmag.com/40th-anniversary/the-changing-demographics-of-america-538284/?no-ist 2. http://www.washingtonpost.com/blogs/wonkblog/wp/2015/01/20/4-maps-that-show-how-demographic-change-will-touch-every-corner-of-the-country/Read MoreArranged Marriage: a Violation of Human Rights?2148 Words   |  9 PagesArranged Marriage: A violation of human rights? Ashley Bowers December 7, 2011 SOCW 510 Introduction Do arranged marriages violate human rights as they are protected by international humanitarian law? Marriage is a vital part of the social and economic life of a person’s life. 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Cultural barriers of male-dominatedRead MoreEarly Marriage9846 Words   |  40 PagesEarly Marriage in South Asia A DISCUSSION PAPER Contents INTRODUCTION 2 THE PREVALENCE OF EARLY MARRIAGE 3 CAUSES OF EARLY MARRIAGE 5 CONSEQUENCES OF EARLY MARRIAGE 8 RESPONSES TO EARLY MARRIAGE OF CHILDREN 16 Introduction Early marriage affects millions of children through the world. It is widely practiced in the countries of South Asia where every year millions of girls-preteens and teens- become the wives of older men. Young girls are marriedRead MoreThe Impact of Population Aging5586 Words   |  23 PagesCHAPTER 1 INTRODUCTION 1.1: Study Background The population aging, in other words, the greying of the population is major concern all over the world. Many factors are leading to population aging, namely, unwillingness to marry, late marriage, fertility control, low birth rate and longer life span. All these factors are also related to developing status of the country. 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Physics Study Notes Hsc Free Essays

string(121) " the velocity is zero and the potential energy is zero because this is where we selected the zero of potential energy\)\." Physics Summary Contents Core Topic One: Space 1. 2. 3. We will write a custom essay sample on Physics Study Notes Hsc or any similar topic only for you Order Now 4. Gravity Space Launch and Return Future Space Travel Special Relativity 2 3 13 14 Page Core Topic Two: Motors and Generators 1. 2. 3. 4. 5. The Motor Effect Electromagnetic Induction Electric Generators Transformers Electric Motors 19 24 27 29 31 Core Topic Three: From Ideas to Implementation 1. 2. 3. 4. Cathode Rays Quantum Theory Solid State Devices Superconductivity 32 37 43 48 Option Topic: Quanta to Quarks 1. . 3. 4. 5. 6. Models of the Atom Quantum Physics The Electron Microscope Applications of Radioactivity Nuclear Applications The Structure of Matter 53 57 59 61 66 67 William Kim HSC Physics Summary | page 1 Core Topic One: Space 1. The Earth has a gravitational field that exerts a force on objects both on it and around it  § Define weight as the force on an object due to a gravitational field The weight of an object is the force of gravity acting on it. r W = mg Where W is the weight in newtons (N), m is the mass in kilograms (kg) and g can be either: 1. The accelerati on due to gravity (= 9. 8 m/s/s at the Earth’s surface); or 2. The gravitational field strength (= 9. 8 N/kg at the Earth’s surface).  § Define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field. As we lift an object from the ground to a height above the ground we do work on it. This work is stored in the object as gravitational potential energy. For an object of mass m at a height h above the Earth’s surface the gravitational potential energy E is given by: E p = mgh However this equation is valid only when the object is near the Earth’s surface. The gravitational potential energy is a measure of the work done in moving an object from infinity to a point in the field. The general expression for the gravitational potential energy of an object of mass m at a distance r from the centre of the Earth (or other planet) is given by: E p = ? G mM E r Newton’s Law of Universal Gravitation m F = G 12 2 r where G is the universal gravitational constant. The Gravitational Field Surrounding any object with mass is a gravitational field. g= Gm r2 Where M is the mass of the Earth (or other planet). Change in Gravitational Potential Energy The change in potential energy of a mass m1 as it moves from infinity to a distance r from a source of a gravitational field (due to a mass m2) is given by: mm ? E p = G 1 2 r Change in Gravitational Potential Energy Near the Earth (when radius increases from A to B) ?1 1? ?E p = GmM E ? ? ? ?r ? ? A rB ? William Kim HSC Physics Summary | page 2 . Many factors have to be taken into account to achieve a successful rocket launch, maintain a stable orbit and return to Earth  § Describe the trajectory of an object undergoing projectile motion within the Earth’s gravitational field in terms of horizontal and vertical components Any moving object that moves only under the force of gravity is a projectile. The horizontal motion of a projectile is independent to the vertical motion. The reason for this result is that gravity is the only force acting on the objects and this always acts towards the centre of the Earth. Projectile motion can be analysed by realising that: 1. The horizontal motion is constant velocity. 2. The vertical motion of constant acceleration (with acceleration of g). Equations of Uniformly Accelerated Motion r r r v = u + at r r 1r s = ut + at 2 2 2 2 v = u + 2 as The Path of a Projectile The velocity at any point of the path of a projectile is simply the vector sum of the horizontal and vertical velocity components at that point. ?y = k (? x ) 2 ? ag ? k =? 2 ? ? 2u ? ? x? The horizontal component is constant. The vertical component changes at g, the acceleration due to gravity. Trajectories The path followed by a projectile – its trajectory – is a parabola (or linear) (1) Horizontal motion: ? x = u x t 1 (2) Vertical motion: ? y = a g t 2 2 From (1): ? x t= ux Combining (2) (3): 1 ? ?x ? 1 ag ? y = a g ? ? = (? x )2 2 ? u ? 2 ? x? 2 ux 2 ux ? y ? x William Kim HSC Physics Summary | page 3  § Describe Galileo’s analysis of projectile motion Galileo was responsible for deducing the parabolic shape of the trajectory of a projectile. Galileo’s analysis of projectile motion led him to consider reference frames. These are what all measurements are compared to. The concept of Galilean relativity refers that the laws of mechanics are the same in a frame of reference that is at rest or one that moves with constant velocity.  § Explain the concept of escape velocity in terms of the: o gravitational constant o mass and radius of the planet If an object is projected upward with a large enough velocity it can escape the gravitational pull of the Earth (or other planet) and go into space. The necessary velocity to leave the Earth (or other planet) is called the escape velocity. Escape velocity depends on the gravitational constant, the mass and radius of the planet. Suppose an object of mass m is projected vertically upward from the Earth’s surface (mass of M and radius R) with an initial velocity u. The initial mechanical energy, that is, kinetic and potential energy is given by: E k i + E pi = 1 M m mu 2 ? G E 2 RE Let us assume that the initial speed is just enough so that the object reaches infinity with zero velocity. The value of the initial velocity for which this occurs is the escape velocity ve . When the object is at infinity the mechanical energy is zero (the kinetic energy is zero since the velocity is zero and the potential energy is zero because this is where we selected the zero of potential energy). You read "Physics Study Notes Hsc" in category "Essay examples" Hence 1 M m mve2 ? G E = 0 which leads to: 2 RE ve = 2GM E RE William Kim HSC Physics Summary | page 4  § Discuss Newton’s analysis of escape velocity Circular Motion The motion of an object in a circular path with constant speed is called uniform circular motion. Although the speed remains the same in uniform circular motion, it follows that an object travelling in a circular path must be accelerating, since the velocity (that is, the speed in a given direction) is continually changing. r r v1 ? v2 v1 = v 2 r v2 r The change in velocity is given by: v2 r r r r v1 ? v = v 2 ? v1 r ? v1 r r ? v r and since: a = ? v r ? t ? v it follows that the object is accelerating. Isaac Newton proposed the idea of artificial satellites of the Earth. He considered how a projectile could be launched horizontally from the top of a high mountain so that it would not fall to Earth. As the launch velocity was increased, the distance that the object would travel before hitting the Earth would increase until such a time that the velocity would be sufficient to put the object into orbit around the Earth. (A higher velocity would lead to the object escaping from the Earth. ) Centripetal Acceleration As can be seen, when the change in velocity is placed in the average position between v1 and v2, it is directed towards the centre of the circle. When an object is moving with uniform circular motion, the acceleration (the centripetal acceleration) is directed towards the centre of the circle. For an object moving in a circle of radius r with an orbital velocity of v, the centripetal acceleration a is given by: v2 ac = r Earth Orbits A satellite can be put into Earth orbit by lifting it to a sufficient height and then giving it the required horizontal velocity so that it does not fall back to Earth. For the satellite to circle the Earth, the centripetal force required is provided by the gravitational attraction between the satellite and the Earth. Hence the centripetal acceleration is given by: v2 g= R William Kim HSC Physics Summary | page 5  § Use the term ‘g forces’ to explain the forces acting on an astronaut during launch g-forces on Astronauts Humans can withstand 4g without undue concern. Accelerations up to ~10g are tolerable for short times when the acceleration is directed parallel to a line drawn between the person’s front and back. The human body is relatively unaffected by high speeds. Changes in speed, however, that is, accelerations, can and do affect the human body creating ‘acceleration stress’. g-forces Acceleration forces – g-forces – are measured in units of gravitational acceleration g. For example, a force of 5g is equivalent to acceleration five times the acceleration due to gravity. If the accelerations are along the body’s long axis then two distinct effects are possible: 1. If the acceleration is in the direction of the person’s head they may experience a ‘black out’ as the blood rushes to their feet; or 2. If the acceleration is towards their feet, they may experience a ‘red out’ where the blood rushes to their head and retina.  § Compare the forces acting on an astronaut during launch with what happens during a roller coaster ride As you ‘fall’ from a height, you experience negative g-forces (you feel lighter). When you ‘pull out’ of a dip after a hill or follow an ‘inside loop’, you experience positive g-forces (you feel heavier). The positive g-forces are like those astronauts experience at lift-off. Consider a rider in a car at the bottom of an inside loop. The rider has two forces acting on them: 1. Their normal weight (mg) acting down; and 2. The ‘normal reaction force’ (N) acting up. This is the push of the seat upwards on their bottom. Assume that the loop is part of a circle of radius R. A centripetal force is required for the rider to travel in a circle. This is the difference between the normal force and the weight force, that is: mv 2 mv 2 N ? mg = : N = mg + R R The g-forces are found from the ‘normal force’ divided by the weight. That is: N = mg mg + mv 2 2 R = 1+ v mg gR N mg g’s felt by rider = William Kim HSC Physics Summary | page 6  § Discuss the impact of the Earth’s orbital motion and its rotational motion on the launch of a rocket A moving platform offers a boost to the velocity of a projectile launched from it, if launched in the direction of motion of the platform. This principle is used in the launch of a rocket by considering that the Earth revolves around the Sun at 107,000km/h relative to the Sun and rotates once on its axis per day so that a point on the Equator has a rotational velocity of approximately 1,700km/h relative to the Sun. Hence, the Earth is itself a moving platform with two different motions which can be exploited in a rocket launch to gain a boost in velocity. Earth Orbit A rocket heading into orbit is launched to the east to receive a velocity boost from the Earth’s rotational motion. An Interplanetary Trip The flight of a rocket heading into space is timed so that it can head out in the direction of the Earth’s motion and thereby receive an extra boost.  § Analyse the changing acceleration of a rocket during launch in terms of the: Law of Conservation of Momentum Forces experienced by astronauts Law of Conservation of Momentum Rocket engines generate thrust by burning fuel and expelling the resulting gases. Conservation of momentum means that as the gases move one way, the rocket moves the other. (Momentum before the burning is zero; hence the momentum after is also zero. The gases carry momentum in one direction down, and so the rocket carries an equal momentum in the opposite direction up. ) As fuel is consumed and the gases expelled, the mass of the system decreases. Since acceleration is proportional to the thrust and inversely proportional to the mass, as the mass decreases, the acceleration increases. Hence the forces on the astronauts increase. Forces Experienced by Astronauts g forces varied during the launch of Saturn V, a large three-stage rocket used to launch the Apollo spacecraft. This is attributed to the sequential shutdown of the multiple rocket engines of each stage – a technique designed specifically to avoid extreme g forces. William Kim HSC Physics Summary | page 7  § Analyse the forces involved in uniform circular motion for a range of objects, including satellites orbiting the Earth Motion Whirling rock on a string Electron orbiting atomic nucleus Car cornering Moon revolving around Earth Satellite revolving around Earth Fc Provided By†¦ The string Electron-nucleus electrical attraction Friction between tyres and road Moon-Earth gravitational attraction Satellite-Earth gravitational attraction  § Compare qualitatively and quantitatively low Earth and geostationary orbits Low Earth Orbit A low Earth orbit is generally an orbit higher than approximately 250 km, in order to avoid atmospheric drag, and lower than approximately 1000 km, which is the altitude at which the Van Allen radiation belts start to appear. The space shuttle utilises a low Earth orbit somewhere between 250 km and 400 km depending upon the mission. At 250 km, an orbiting spacecraft has a velocity of 27,900km/h and takes just 90 minutes to complete an orbit of the Earth. Geostationary Orbit A geostationary orbit is at an altitude at which the period of the orbit precisely matches that of the Earth. If over the Equator, such an orbit would allow a satellite to remain ‘parked’ over a fixed point on the surface of the Earth throughout the day and night. From the Earth such a satellite appears to be stationary in the sky, always located in the same direction regardless of the time of day. This is particularly useful for communications satellites because a receiving dish need only point to a fixed spot In the sky in order to remain in contact with the satellite. The altitude of such an orbit is approximately 38,800 km. If a satellite at this height is not positioned over the Equator but at some other latitude, it will not remain fixed at one point in the sky. Instead, from the Earth the satellite will appear to trace out a ‘figure of eight’ path each 24 hours. It still has a period equal to the Earth’s, however, and so this orbit is referred to as geosynchronous. William Kim HSC Physics Summary | page 8  § Discuss the important of Newton’s Law of Universal Gravitation in understanding and calculating the motion of satellites Using Newton’s Law of Universal Gravitation combined with the expression for centripetal force, we can see that the orbital velocity required for a particular orbit depends nly on the mass of the Earth, the radius of the Earth and the altitude of the orbit (distance from the surface of the Earth). Given that the mass and radius of the Earth have fixed values, this means that altitude is the only variable that determines the specific velocity required. In addition, the greater the radius of the orbit, the lower the orbital velocity required. Once a launched rocket has achieved a suff icient altitude above the surface of the Earth, it can be accelerated into an orbit. It must attain a specific speed that is dependent only upon the mass and radius of the Earth and the altitude above it. If that speed is not reached, the spacecraft will spiral back in until it re-enters the atmosphere; if the speed is exceeded, it will spiral out. This can be considered by appreciating that the simplest orbital motion is a uniform speed along a circular path around the Earth. Uniform circular motion, as already mentioned, is a circular motion with a uniform orbital velocity. According to Newton’s First Law of Motion, a spacecraft in orbit around the Earth, or any object in circular motion, requires some force to keep it there, otherwise it would fly off at a tangent to the circle. This force is directed back towards the centre of the circle. In the case of spacecraft, it is the gravitational attraction between the Earth and the spacecraft that acts to maintain the circular motion that is the orbit. The force required to maintain circular motion, known as centripetal force, can be determined using the following equation: mv 2 FC = r The application of Newton’s Law of Universal Gravitation to the orbital motion of a satellite will produce an expression for the critical orbital velocity mentioned earlier. Recall that this law states that the gravitational attraction between a satellite and the Earth would be given by the following expression: m m FG = G E 2 S r This gravitational force of attraction also serves as the centripetal force for the circular orbital motion, hence: FG = FC Therefore, we can equate the formula for FG with that for FC: m E mS m S v 2 G = r r2 ? v = GmE r where v = orbital velocity (ms-1) where r = rE + altitude (m) William Kim HSC Physics Summary | page 9 Kepler’s Third Law: The Law of Periods Further, we can use the expression for orbital velocity to prove Kepler’s Third Law – the Law of Periods. The period or the time taken to complete one full orbit can be found by dividing the length of the orbit (the circumference of the circle) by the orbital velocity, v. 2? r T= v Changing the subject of this expression to v and then substituting into the formula for v given above: 2? r Gm E = T r 3 Gm E r ? 2 = T 4? 2 This means that for any satellite of the Earth at any altitude, the ratio r3:T2 always equals the same fixed value. William Kim HSC Physics Summary | page 10  § Describe how a slingshot effect is provided by planets for space probes Many of today’s space probes to distant planets such as Jupiter use a gravitational ‘slingshot’ effect (also known as a gravity-assist trajectory) that brings the probe close to other planets to increase the probe’s velocity. In 1974, Mariner 10 was directed past Venus on its way to Mercury. The Pioneer and Voyager probes also used this method. Consider a trip to Jupiter such as the Galileo probe that involved a single fly-by of Venus and two of the Earth. As the probe approaches Venus, it is accelerated by Venus’ gravitational attraction, causing it to speed up relative to Venus. By Newton’s Third Law, Venus will also experience a force slowing it down. It’s mass, however, is so much greater than that of the probe that the velocity decrease is imperceptible. ) As the probe passes Venus, its speed is reduced (relative to Venus). Relative to the Sun, however, its speed has increased. The probe picks up angular momentum from the planet (w hich loses an equal amount of an angular momentum). Gravity allows the ‘coupling’ between the probe and planet to facilitate the transfer. For this reason, gravity-assist trajectories should more correctly be called angular momentum-assist trajectories. f = vi + 2Vi Planet vi Spacecraft Vi Vf  § Account for the orbital decay of satellites in low Earth orbit All satellites in low Earth orbit are subject to some degree of atmospheric drag that will eventually decay their orbit and limit their lifetimes. As a satellite slows, it loses altitude and begins a slow spiral downwards. As it descends, it encounters higher density air and higher drag, speeding up the process. By the time the satellite is below an altitude of 200 km it has only a few hours left before colliding with the Earth. The re-entry process generates much heat and most satellites burn up (vaporise) before impacting. William Kim HSC Physics Summary | page 11  § Discuss issues associated with safe re-entry into the Earth’s atmosphere and landing on the Earth’s surface There are significant technical difficulties involved in safe re-entry, the most important being: 1. The heat generated as the spacecraft contacts the Earth’s atmosphere; and 2. Keeping the retarding-forces (g-forces) within safe limits for humans. Heating Effects The Earth’s atmosphere provides aerodynamic drag on the spacecraft and as a result high temperatures are generated by friction with air molecules. Identify that there is an optimum angle for re-entry into the Earth’s atmosphere and the consequences of failing to achieve this angle. g-Forces The angle of re-entry is critical: too shallow and the spacecraft will bounce off the atmosphere back into space; too steep and the g-forces will be too great for the crew to survive (and the temperatures generated with the atmosphere will be too high even for the refracting materials used). The ‘allowed’ angle of re-entry is –6. 2 °  ± 1 ° relative to the Earth’s horizon. William Kim HSC Physics Summary | page 12 3. Future space travel and exploration will entail a combination of new technologies based on current and emerging knowledge  § Discuss the limitation of current maximum velocities being too slow for extended space travel to be viable Scientists have not yet been able to produce speeds of spacecraft more than a few tens of thousands of kilometres per hour. When travelling to distant planetary objects, the engines of spacecraft are not on as spacecraft rely on inertia to move along. To increase the speed significantly would require the engines to be operating, which would require more fuel. More fuel would require more thrust putting the spacecraft into orbit, which would require more fuel and so on. To increase the speed of spacecraft to values that would make interplanetary travel feasible requires a whole new technology (one not based on the emission of gases produced by combustion). Clearly, while current maximum velocities are just adequate for interplanetary travel, they are entirely inadequate for interstellar travel.  § Describe difficulties associated with effective and reliable communications between satellites and earth caused by: – distance – van Allen radiation belts – sunspot activity Distance Microwaves and radio waves, like all EM waves, travel through space at the speed of light. This is the fastest speed possible in our universe and therefore places a limit on the speed and response time of space communications. The immense distance involved in space communications creates a distance-related time lag. Also, as EM radiation obeys an inverse square law, there is a loss of signal strength as distance increases. This is referred to as space loss. Van Allen radiation belts There are two belts of energetic charged particles, mainly electrons and protons, lying at right angles to the equator of the Earth. Some of the solar wind particles become trapped in the Van Allen radiation belts. Intense solar activity can disrupt the Van Allen Belts. This in turn is associated with auroras and magnetic storms. The charged particles drifting around the Earth in the outer belt corresponds to an electric current and hence has an associated magnetic field. Once or twice a month this current increases and as a result its magnetic field increases. This can lead to interference of short wave radio communication, errors in communication satellites and even failure of electrical transmission lines. Sunspot activity Sunspots are associated with the solar wind (consisting of a stream of charged particles). The solar wind affects the Earth’s magnetic field and this in turn affects radio communication. William Kim HSC Physics Summary | page 13 4. Current and emerging understanding about time and space has been dependent upon earlier models of the transmission of light  § Outline the features of the ether model for the transmission of light It was believed that light waves require a medium to propagate. Although nobody could find such a medium, belief in its existence was so strong that it was given a name – the ether. The ether: – Filled all of space, had low density and was perfectly transparent – Permeated all matter and yet was completely permeable to material objects – Had great elasticity to support and propagate the light waves  § Describe and evaluate the Michelson-Morley attempt to measure the relative velocity of the Earth through the ether The Ether Wind Because the Earth was moving around the Sun, it was reasoned that an ether wind should be blowing past the Earth. However, if a wind blows, the speed of sound relative to the stationary observer would vary. Thus it was believed that the speed of light should vary due to the presence of the â€Å"ether wind†. It was in an attempt to detect this difference that Michelson and Morley did their famous experiment. The Michelson-Morley Experiment Light sent from S is split into two perpendicular beams by the half-silvered mirror at A. These two beams are then reflected back by the mirrors M1 and M2 and are recombined in the observer’s eye. An interference pattern results from these two beams. The beam AM1 travelled across the ether, whilst AM2 travelled with and against the ether. The times to do this can be shown to be different and so introduce a phase difference between the beams. When the entire apparatus was rotated through 90 °, a change in the interference pattern was expected. None was observed. The result of the Michelson-Morley experiment was that no motion of the Earth relative to the ether was detectable. M1 A S M2 Ether Wind  § Discuss the role of critical experiments in science, such as Michelson-Morley’s, in making determinations about competing theories From a hypothesis, predictions are made of what should happen if a particular experiment is performed. If the results are not in agreement with the prediction, the hypothesis is incorrect. As we have seen, the fact that a null result was found from this experiment showed the ether hypothesis to be invalid. This opened up a completely revolutionary view of space and time with the work of Einstein. William Kim HSC Physics Summary | page 14  § Outline the nature of inertial frames of reference Frames of Reference Frames of reference are objects or coordinate systems with respect to which we take measurements. Position In maths, the Cartesian coordinate system is used and position is referred to the axes x, y and z. In experiments in class, the laboratory is the frame of reference. S S’ r u r P v Velocity An object P travels with velocity v with respect to a reference frame S. Another frame S’ moves with velocity u relative to S. The velocity of P relative to S’ is v’ = v – u. Velocity thus depends upon the reference frame. Inertial Frames of Reference An inertial frame of reference is one that is moving with constant velocity or is at rest (the two conditions being indistinguishable). In such reference frames, Newton’s Law of Inertia holds. A non-inertial frame of reference is one that is accelerating.  § Discuss the principle of relativity Three hundred years before Einstein, Galileo posed a simple idea, now called the principle of relativity, which states that all steady motion is relative and cannot be detected without reference to an outside point. This idea can be found built into Newton’s First Law of Motion as well. Two points to be reinforced:  § The principle of relativity applies only for non-accelerated steady motion  § This principle states that within an inertial frame of reference you cannot perform any mechanical experiment or observation that would reveal to you whether you were moving with uniform velocity or standing still. William Kim HSC Physics Summary | page 15  § Identify the significance of Einstein’s assumption of the constancy of the speed of light In 1905, Albert Einstein proposed that the speed of light is constant and is independent of the speed of the source or the observer. This premise explained the ‘negative’ result of the MichelsonMorley experiment and showed that the ether concept was not needed. As a consequence of this ‘law of light’ it can be shown that there is no such thing as an absolute frame of reference. All inertial reference frames are equivalent. That is, all motion is relative. The laws of physics are the same in all frames of reference; that is, the principle of relativity always holds.  § Recognise that if c is constant then space and time become relative In Newtonian physics, distance and velocity can be relative terms, but time is an absolute and fundamental quantity. Einstein radically altered the assumptions of Newtonian physics so that now the speed of light is absolute, and space and time are both relative quantities that depend upon the motion of the observer. (Our reality is what we measure it to be. Reality and observation cannot be separated. Remember this as we proceed).  § Discuss the concept that length standards are defined in terms of time with reference to the original meter †¦In other words, the measured length of an object and the time taken by an event depend entirely upon the velocity of the observer. (This is why our current standard of length is defined in terms of time – the metre is the distance travelled by light in a vacuum in the fraction 1/299792458 of a second).  § Identify the usefulness of discussing space/time, rather than simple space †¦Further to this, since neither space nor time is absolute, the theory of relativity has replaced them with the concept of a space-time continuum. Space and time, not just space, are relative quantities).  § Account for the need, when considering space/time, to define events using four dimensions †¦Any event then has four dimensions (three space coordinates plus a time coordinate) that fully define its position within its frame of reference. William Kim HSC Physics Summary | page 16  § Explain qualitatively and quantitatively the consequence of special relativity in relation to: The relativity of simultaneity The equivalence between mass and energy Length contraction Time dilation The Relativity of Simultaneity (simultaneity and the velocity of light) Observers in relative motion will disagree on the simultaneity of events separated in space. The Equivalence Between Mass and Energy The mass of a ‘moving’ object is greater than when it is ‘stationary’ – it experiences mass dilation (covered later). Since c is the maximum speed in the universe it follows that a steady force applied to an object cannot continue to accelerate. It follows that the inertia, that is the resistance to acceleration, must increase. But inertia is a measure of mass and so the mass has increased. It is this increase in mass that prevents any object from exceeding the speed of light, because as it accelerates to higher velocities its mass increases, which means that further accelerations will require even greater force. This is further complicated by time dilation because, as speeds increase to near light speed, any applied force has less and less time in which to act. The combined effect is that as mass becomes infinite and time dilates, an infinite force would be required to achieve any acceleration at all. Sufficient force can never be supplied to accelerate beyond the speed of light. If force is applied to an object, then work is done on it – energy is given to the object. This energy would take the form of increased kinetic energy as the object speeds up. But at near light speed the object does not speed up. The applied force is giving energy to the object and the object does not acquire the kinetic energy we would expect. Instead, it acquires extra mass. Einstein made an inference here and stated that the mass (or inertia) of the object contained the extra energy. Relativity results in a new definition of energy as follows: E = E k + mc 2 where E = total energy, Ek = kinetic energy, m = mass, c = speed of light When an object is stationary, it has no kinetic energy, but still has some energy due to its mass. This is called its mass energy or rest energy and is given by: 8 -1 E = mc 2 where E = rest energy (J), m = mass (kg), c = speed of light (3 x 10 m s ) William Kim HSC Physics Summary | page 17 Implications of Special Relativity: To measure speed we need to measure distance and time. If c remains constant, then it follows that distance (length) and time must change. Space and time are relative concepts. Length Contraction (the Lorentz-FitzGerald Contraction) The length of a ‘moving’ rod appears to contract in the direction of motion relative to a ‘stationary’ observer. l = l0 1 ? v2 c2 where l is the moving length, l0 is the ‘rest’ length (that is, the length as measured by an observer at rest with respect to the rod) and v is the speed of the rod. Time Dilation Time in a ‘moving’ frame appears to go slower relative to a ‘stationary’ observer t= t0 1? v c2 2 where t is the observed time for a ‘stationary’ observer and t0 is the time for an observer travelling in the frame. 0 is called the proper time (this is the time measured by an observer present at the same location as the events that indicate the start and end of an event). Mass Dilation The mass of a ‘moving’ object is greater than when it is ‘stationary’. m= m0 1? v2 c2 where m is the m ass for a ‘moving’ object and m0 is the mass for that object when it is ‘stationary. ’  § Discuss the implications of time dilation and length contraction for space travel The relativity of time allows for space travel into the future but not into the past. When travelling at relativistic speeds (0. 1c or faster), relativity influences the time that passes on the spacecraft. Astronauts on a relativistic interstellar journey would find their trip has taken fewer years than observed on Earth. William Kim HSC Physics Summary | page 18 Core Topic Two: Motors and Generators 1. Motors use the effect of forces on current-carrying conductors in magnetic fields  § Identify that moving charged particles in a magnetic field experience a force Charged particles moving in an external magnetic field will experience a force. If the moving charged particles are flowing through, and confined within, a conductor that is in an external magnetic field, the conductor will also experience a force. This effect is known as the motor effect. F = qvB Use left hand â€Å"FBI gun† An example: Van Allen Radiation Belts The Earth’s magnetic field captures charged particles from the solar wind (low energy) and cosmic rays (high energy). The charges are force to spiral along the field lines accumulating into two doughnut-shaped belts of â€Å"radiation† called the upper and lower Van Allen radiation belts. William Kim HSC Physics Summary | page 19  § Discuss the effect, on the magnitude of the force on a current-carrying conductor, of variations in: The strength of the magnetic field in which it is located The magnitude of the current in the conductor The length of the conductor in the external magnetic field The angle between the direction of the external magnetic field and the direction of the length of the conductor †¦The force is proportional to the magnetic field strength, B †¦The force is proportional to the current, I †¦The force is proportional to the length, L The force is at a maximum when the conductor is at right angles to the field, and is zero when the conductor is parallel to the field. The magnitude of the force is proportional to the component of the field that is at right angles to the conductor. F = BIl sin ? William Kim HSC Physics Summary | page 20  § Describe qualitatively and quantitatively the force on long parallel current-carrying conductors : Ampere’s Law Two parallel wires, each carrying a current, will exert a force on the other. This happens because each current produces a magnetic field (as in Oersted’s experiment). Therefore each wire finds itself carrying a current across the magnetic field produced by the other wire and hence experiences a force. Determining the magnitude of the force between two parallel conductors The magnetic field strength at a distance, d, from a long straight conductor carrying a current, I, can be found using the formula: kI B= d -7 -2 where k = 2. 0 x 10 N A The magnitude of the force experienced by a length, l, of a conductor due to to an external magnetic field is: F = I 2 lB or ? kI ? F = I 2l ? 1 ? ? d ? rearranged F II =k 1 2 l d F II =k 1 2 l d (Ampere’s law) I1 I2 If currents are in the same direction, then the conductors will attract. If currents are in opposite directions, then the conductors will repel. William Kim HSC Physics Summary | page 21  § Define torque as the turning moment of a force using: Torque is turning force. Its’ units are Newton-metres (Nm). ? = Fd where ? = torque, in Nm F = force, in N D = distance from rotational axis, in m F = BIl ? =BIld Rotational axis d ? = Fd  § Identify the forces experienced by a currentcarrying loop in a magnetic field and describe the net result of the forces b max ? = nBIA zero ? b Current Loops N I F = BIl ? =BIld ? = ? 1 + ? 2 = BIld + BIld = 2 BIld = BI (l ? 2d ) = BIA S ? = nBIA cos ? ? b (For each turn of the loop) Generally, ? =nBIA cos ? William Kim HSC Physics Summary | page 22  § Account for the motor effect due to the force acting on a current-carrying conductor in a magnetic field The motor effect Recall that charged particles moving in an external magnetic field will experience a force. If the moving charged particles are flowing through, and confined within, a conductor that is in an external magnetic field, the conductor will also experience a force. An electric motor is a device that transforms electrical potential energy into rotational kinetic energy.  § Describe the main features of a DC electric motor  § Discuss the importance of the invention of the commutator for developing electric motors  § Describe the role of the metal split ring and the brushes in the operation of the commutator Anatomy of a DC motor – Permanent magnets: provide an external magnetic field in which the coil rotates. As the magnets are fixed, they are known as the stator. – Rotating coil: carries a direct current that interacts with the magnetic field, producing torque. Armature: is made of ferromagnetic material and allows the coil to rotate freely on an axle. The armature and coil together are known as the rotor. The armature protrudes from the motor casing, enabling the movement of the coil to be used to do work. – Commutators: reverse the current of the coil every half turn to maintain consistent direction and torque. It i s a mechanical switch that automatically changes the direction of the current flowing through the coil when the torque falls to zero. – Brushes: maintain electrical contact of coils with the rest of the circuit. The development of DC motors outstripped that of AC motors and generators for two reasons: – Voltaic batteries could supply power – They could use powerful electromagnets that were far stronger than permanent magnets The development of the commutator was important because it led to the development of modern electric motors and generators. It enabled motors to provide steady circular motion of a drive shaft.  § Describe how the required magnetic fields can be produced either by currentcarrying coils or permanent magnets The magnetic field of a DC motor can be provided either by permanent magnets or by electromagnets. William Kim HSC Physics Summary | page 23 2. The relative motion between a conductor and magnetic field is used to generate an electrical voltage  § Outline Michael Faraday’s discovery of the generation of an electric current by a moving magnet Faraday had found that 3 things are necessary to generate (or â€Å"induce†) an EMF (voltage supply): – A magnetic field (from some magnets or electromagnet) – A conductor (eg. wire or coil of wire) – Relative motion / change between the field and the conductor If the conductor formed a closed loop then an induced current would also flow. ire If this wire is dropped so that it cuts flux lines, then a voltage appears between the ends because electrons are forced to the right. They eventually stop moving because they create an electric field pushing them back. As long as the magnet is moving, an emf and current is induced. Faraday’s Law ? =? n ? where ? = induced EMF, in V n = number of turns on coil ? = change in ? = magnetic flux, in Wb = BA B = magnetic flux density (field strength), in T The induced voltage can be increased by: Increasing n: more turns on the coil Increasing B: use strong magnets Increasing A: use a bigger coil Decreasing t: go faster! B A = area of coil in m 2 ? = time taken for to occur William Kim HSC Physics Summary | page 24  § Define magnetic field strength B as magnetic flux density Magnetic flux density is the magnetic flux per unit area and is a measure of the magnetic field strength.  § Explain the concept of magnetic flux in terms of magnetic flux density and surface area ? = BA sin ? where B = magnetic flux density, in T A = area, in m 2 ? = magnetic flux, in Wb  § Explain generated potential difference as the rate of change of magnetic flux through a circuit The induced emf is proportional to the rate of change of flux through the circuit. See Faraday’s Law (above).  § Account for Lenz’s Law in terms of conservation of energy and relate it to the production of back emf in motors Lenz’s Law This is a supplementary law to Faraday’s Law. It says that any induced emf or current will have a direction that opposes the change that caused it. This is really just a restatement of the law of conservation of energy because the induced electrical energy has come from the thing that causes the original motion. Eg. In a hydroelectric power station, the kinetic energy of flowing water is converted into electrical energy. N William Kim HSC Physics Summary | page 25  § Explain that, in electric motors, back emf opposes the supply emf Back emf Back emf is generated in any coil that experiences changing B fields, even though it is producing them. Note that back emf is frequency dependent – the higher the frequency of the changing field, the greater the back emf produced. Back emf is also produced in the rotating coil of a motor: – When the motor is spinning at its operating speed, back emf will have its max value, but†¦ – When the motor is just turned on it isn’t spinning yet so there is no back emf. This can lead to excessive current so the motor may be protected by using a â€Å"starting resistance† that limits current. When up to speed the resistor is taken out of the circuit. The coil becomes an electromagnet and generates an alternating B field BUT it also experiences the changing B field and generates its own emf that opposes the applied emf.  § Apply Lenzà ¢â‚¬â„¢s Law to the production of eddy currents Eddy Currents – are induced currents (usually unwanted or unintended) in two-dimensional conductors (eg. sheet metal) or three-dimensional conductors (eg. a block of steel). Sometimes it is necessary to design against them. Eg. the core of a motor is made of soft iron, and is made of thin layers (laminated) to prevent eddy currents. Some devices rely on eddy currents to work: Electromagnetic braking – a moving conductor near magnets will slow down because the eddy currents oppose its motion. Electromagnetic switching – security ‘gates’ that are really coils with AC generate a high frequency B field. Metal in this field develops eddy currents that work against the field, slowing it down. A detector circuit picks up on this and sets off an alarm. Induction Cooktops- are an application of Faraday’s Law. Instead of a heating element, this cooktop contains a set of coils with alternating current passing through them. This produces a changing B field above the cooktop. A metal saucepan placed on the cooktop is a conductor in the changing B field and therefore an electric current is induced in the base of the pan. The current heats the pan, and this heat cooks the food. Induction cooktops are approximately twice as efficient as a gas cooktop, but are expensive to purchase. William Kim HSC Physics Summary | page 26 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Movement of metal Eddy current loop 3. Generators are used to provide large scale power production in isolated areas and as a backup in emergency situations  § Identify the main components of a generator An electric generator (dynamo) is a device that includes all of the elements necessary to transform mechanical kinetic energy to electricity according to Faraday’s Law: – A magnetic field (provided by a set of permanent magnets); – A conductor (a coil mounted on an axle, so it can spin); – Relative motion (the coil is made to spin by some other form of energy). Compare the structure and function of a generator to an electric motor In fact, most generators are constructed just like a motor, however the flow of energy through them is different. Motor: electrical energy a kinetic energy Generator: kinetic energy a electrical energy  § Describe the operation of an AC and a DC generator EMF is generated in the coil and a circuit is completed to the outside world through ring connectors, just like motors. If standard slip rings are used then a dynamo naturally produces alternating current AC. I t E t Doubling the frequency of rotation doubles the maximum induced emf If a split ring commutator is used instead, then the direction of the current flowing from the coil is reversed every ? c ycle. This produces a pulsing type of direct current DC. + I t William Kim HSC Physics Summary | page 27  § Discuss the energy losses that occur as energy is fed through transmission lines from the generator to the consumer Analyse the effects of the development of AC and DC generators on society and the environment Even good electrical conductors like copper used to supply electricity, sometimes through considerable cable lengths to towns and cities, generate substantial resistances. It follows that to minimise energy loss in the wires, the current needs to be kept low (heating losses vary as the square of the current). This is achieved by transmitting the energy at high voltages.  § Impact on society – Impact on environment – Positive Improved lifestyle Street lighting Electric trains Communication Computerisation of many systems eg. anking, stock market Industrial development a more jobs Lots of electric trains have reduced pollution from steam trains and made public transport more available Electricity has replaced older, more-polluting technologies eg. electrical heating instead of coal burning in fireplaces – Negative Possible risk of cancer living near distribution cables Longer working hours Reliance on electricity leaves us vulnerable to systems loss due to electr ical failure – – – Burning coal in power stations produces smoke and CO2 (a greenhouse gas) Nuclear power stations produce radioactive water have a risk of nuclear accident Hydroelectric schemes redirect water away from river habitats Mining impacts negatively on environment Visual pollution of cables  § Assess evidence about the physiological effects on humans living near high voltage power lines 1979 study found children living near high voltage power lines appeared to develop a particular form of cancer. 997 study showed no evidence of an increase risk of childhood cancer at residential magnetic field levels. 1998 panel stated that EM fields should be considered â€Å"possible human carcinogens† and that there is â€Å"no conclusive and consistent evidence that EM fields cause any human disease. † William Kim HSC Physics Summary | page 28 4. Transformers allow generated voltage to be either increased or decreased before it is used  § Explain the purpose and principles of transform ers in electrical circuits A transformer is a device that alters the voltage and current of an electricity supply. The AC voltage source produces an alternating current in the primary coil. This produces an alternating B field that threads through the secondary coil. The secondary coil now has: – Conductor – B field – Change and therefore generates its own voltage. If there is a closed loop then an alternating current will flow as well.  § Compare step-up and stepdown transformers Step-up transformers: increase voltage and decrease current Step-down transformers: decrease voltage and increase current  § Determine the relationship between the ratio of the number of turns in the primary and secondary coils and the ratio of primary to secondary voltage Vp = primary voltage (voltage in) Ip = primary current np = number of turns on primary coil Vs = secondary voltage (voltage out) Is = secondary current ns = number of turns on secondary coil Vp Vs = np ns If 100% efficient (this needs perfect â€Å"flux linkage†, usually using an iron core) then: Power in primary = Power in secondary ? V p I p = Vs I s ? ? Vp Vs Vp Vs = = Is Ip np ns = Is Ip William Kim HSC Physics Summary | page 29  § Explain why voltage transformations are related to the conservation of energy The Principle of Conservation of Energy states that energy cannot be created or destroyed but that it can be transformed from one form to another. This means that if a step-up transformer gives a greater voltage at the output, its current must be decreased: i. e. power in = power out.  § Explain the role of transformers in electricity sub-stations NSW power stations produce electricity with a voltage of about 23,000 V and a current of about 30,000 A. Unfortunately, this amount is too high to be sent through a cable. This is because it heats the cable causing energy loss. This is called joule heating and happens because: P = I2R So to reduce joule heating, the current must be reduced as much as possible with a step-up transformer. Additional transformers between the power station and consumer (in sub-stations) gradually stepdown the voltage, to 240 V by the time it gets to household users. This is because at high voltages, electricity can conduct through air, making it dangerous for use in the home. Discuss why some electrical appliances in the home that are connected to the mains domestic power supply use a transformer Most electronic circuits are designed to operate at low DC voltages of between 3 V and 12 V. Therefore, household appliances that have electronic circuits in them will have either a plug-in transformer or an inbuilt transformer to step down the domestic 240 V supply. These transformers also have a rectifier circuit built into them that converts AC to DC. TVs also contain a step-up transformer for producing the high voltages needed for the CRT.  § Analyse the impact of the development of transformers on society The development of the generator and transformer has allowed for the setting up of national power grids in almost every country, making that most convenient and flexible form of energy, electricity, accessible from many miles away. The transformer’s role is to step voltage up and down to make efficient transportation and distribution possible. William Kim HSC Physics Summary | page 30 5. Motors are used in industries and the home usually to convert electrical energy into more useful forms of energy  § Describe the main features of an AC electric motor AC induction motor: – The rotor – end rings short circuit non-ferrous rotor bars, that is sealed i. e. no external connections at all (usually a â€Å"squirrel cage†). Encased in a laminated iron armature. – The stator – surrounding electromagnet. – Connection to stator – the surrounding electromagnet receives the AC. In an AC induction motor, the principle of operation is: 1. AC to surrounding electromagnet, which†¦ 2. Produces an oscillating (rotating) B field, which†¦ 3. Induces a current in the rotor, which†¦ 4. Turns the rotor into an electromagnet that†¦ 5. Tries to oppose the field being generated by the stator. 6. The stator and the rotor push against each other (using their B fields), which†¦ 7. Causes the rotor to turn! Brilliant! AC (synchronous) motor: – A rotating coil – Surrounding magnets – Connection to coil via slip rings (commutator for DC motor)  § Explain that AC motors usually produce low power and relate this to their use in power tools Power is the rate of work. Work is done when energy is transformed from one type to another. Induction motors are considered to produce low power because the amount of mechanical work they achieve is low compared with the electrical energy consumed. The ‘lost power’ of induction motors is consumed in magnetising the working parts of the motor and in creating induction currents in the rotor. AC induction motors are considered to be unsuitable for use in heavy industry because their low power rating would make them too expensive to run when performing a specific task. However, they are used extensively in power tools and electric domestic appliances where the loss of power is not economically significant. Explain the advantages of induction motors Advantages of AC induction motors: 1. Simplicity of design; 2. High efficiency (hence low maintenance – there are no brushes or commutators to wear out); 3. Relatively low cost William Kim HSC Physics Summary | page 31 Core Topic Three: From Ideas to Implementation 1. Increased understandings of cathode rays led t o the development of television  § Explain that cathode ray tubes allowed the manipulation of a stream of charged particles Discharge Tubes – Investigation of vacuum tubes could not occur until good vacuum pumps had been invented. A vacuum tube is a glass tube fitted with an electrode at either end, and almost all of the air sucked out. – The positive electrode is the â€Å"anode†; The negative electrode is the â€Å"cathode†. When a high voltage is connected between the electrodes, an invisible ray travels from the cathode to the anode. They were called â€Å"cathode rays†. Cathode rays cause glass to glow green. – A discharge tube is a cathode ray tube with a vacuum pump fitted, so that the air pressure inside the tube can be varied. At different air pressures, different bright effects appear in the tubes e. . bands, striations and dark spaces. These are caused by cathode rays striking atoms in the air inside the tube. The atoms become excited then release photons of visible light – A beam of electrons travels from the cathode to the anode and can be deflected by electrical and/or magnetic fields. Anode Glass glows here Cathode  § Explain why the apparent inconsist ent behaviour of cathode rays caused debate as to whether they were charged particles or electromagnetic waves In 1892 Hertz demonstrated that cathode rays could penetrate thin metal foils. This he believed supported a wave nature. In 1895 Jean-Baptise Perrin showed that cathode rays deposited negative charges on impact with an object, suggesting a particle nature. There was controversy over the nature of cathode rays – waves or particles. William Kim HSC Physics Summary | page 32  § Identify that charged plates produce an electric field If metal plates are separated by a distance and are attached to a power source, an electric field will be produced between them. E = V/d  § Describe quantitatively the force acting on a charge moving through a magnetic field Recall that the force (F) acting on a charge (q) moving with a velocity (v) at an angle to a magnetic field (B), is given by: FB = qvB Where FB = magnetic force (N) q = charge (C) v = velocity of charge (ms-1) B = magnetic field strength (T)  § Discuss qualitatively the electric field strength due to a point charge, positive and negative charges and oppositely charged parallel plates. Describe quantitatively the electric field due to oppositely charged parallel plates ++++++++ If a positive charge is placed near another positive charge, it will experience a force of repulsion. A positive charge placed in a field will experience a force in the direction of the arrow. A negative charge placed in a field will experience a force opposite to the direction of the arrow.  § FE = qE Where FE = electric force (N) q = charge (C) E = electric field strength (NC-1) ———– William Kim HSC Physics Summary | page 33  § Outline Thomson’s experiment to measure the charge/mass ratio of an electron Cathode ray particles ? v? B ? ? ? ? ? ? ? FM ? ? FE ? ? ? v? E ? ? ? J. J. Thomson’s Experiment – By fitting plates to his CRT, he could subject the cathode rays to an electric field. The rays deflected, proving that they were charged particles, not electromagnetic waves. – He noticed that the rays deflected toward the positive plate, proving that they were negatively charged particles. – By crossing electric and magnetic fields, Thomson was able to deduce the velocity of the cathode rays. By turning off the E field, the particles followed a circular arc caused by the B field. The magnetic force was acting like a centripetal force. mv qvB = r q v ? = m Br – 2 ? FM = FE qvB = qE E ? v = B Thomson adjusted the strength of the fields so that the particles were not deflected. By carefully measuring the strength of the fields, Thomson could calculate v. Thomson had already measured B and worked out v. By measuring the radius of curvature r, he could then calculate q/m, i. e. the charge/mass ratio of an electron. q/m for these particles was 1800 times greater than for a hydrogen ion, the simplest known atomic ion. Thomson quickly compared the charges and found them to be about the same (though opposite in sign) Therefore mass for cathode ray particles was 1800 times smaller than hydrogen Therefore cathode ray particles were subatomic particles! This was the first discovery of subatomic particles They were later called electrons. William Kim HSC Physics Summary | page 34  § Outline the role in a cathode ray tube of: Electrodes in the electrode gun The electric field The fluorescent screen The Cathode Ray Tube Each CRT has a vacuum tube/chamber, a cathode, an anode, and a target. Electrodes in the electron gun The electron gun produces a narrow beam of electrons. It consists of a filament, a cathode and two open-cylinder anodes. The anodes help to accelerate and focus the electrons. A ring shaped electrode – the grid – between the cathode and anodes controls the brightness of the spot by controlling the number of electrons emitted by the gun. By making the grid negative with respect to the cathode the number of electrons, and hence the brightness is reduced. The electric field Acts as a deflection system. It consists of two sets of parallel plates connected to a parallel plates connected to a potential difference. This produces an electric field between the plates. The Y-plates control the vertical deflection and the X-plates the horizontal deflection. The fluorescent screen The inside glass of the end of the tube is coated with a fluorescent material for example, zinc sulphide. When an electron beam hits the screen, the coating fluoresces and a spot of light is seen on the screen. The screen acts as a detector of cathode rays. Electrons Cathode Anode To plates and screen William Kim HSC Physics Summary | page 35  § Outline applications of cathode rays in oscilloscopes, electron microscopes and television sets The Cathode Ray Oscilloscope (CRO) Is an electronics diagnostics device because it can show a graph of how voltages vary over time. Deflection of the electron beam is achieved by two sets of plates. Horizontal plates cause vertical deflection while vertical plates cause horizontal deflection. TV Tube An electron gun again produces the electron beam. Coils are used instead of plates, however. Electric current through the coils produce magnetic fields that can deflect the beams quickly from side to side, and more slowly from bottom to top. In this way the beam scans the entire screen. By varying the intensity of the beam, a picture is built up. The picture is refreshed 50 times / second, which is too fast to be noticed by the human eye. The Electron Microscope Uses electrons instead of light. Their wavelength is 100,000 times smaller than visible light, therefore their resolving power is 100,000 times greater. – A â€Å"sample† is placed inside the chamber (which is really the CRT) – The air is then sucked out – An electron gun produces the electron beam – Coils produce magnetic fields to focus the beam (â€Å"magnetic lenses†) – The beam scans over the surface of the sample – Detectors pick up the reflected and scattered electron beam, and from this information a 3 dimensional image is constructed  § Discuss the impact of increased understandings of cathode rays and the development of the oscilloscope on experimental physics The introduction of electronic control systems into all forms of science and industry has seen the cathode ray oscilloscope (CRO) become one of the most widely utilised test instruments. Because of its ability to make ‘voltages’ visible, the cathode ray oscilloscope is a powerful diagnostic and development tool. William Kim HSC Physics Summary | page 36 2. The reconceptualisation of the model of light led to an understanding of the photoelectric effect and black body radiation  § Explain qualitatively Hertz’s experiments in measuring the speed of radio waves and how they relate to light waves Recall: Maxwell’s theory of electromagnetic waves In 1864 Maxwell, through a set of four brilliant equations, predicted a range of invisible waves made up of an electric and magnetic wave that regenerate each other. The speed of these waves was calculated to be 3 x 108 ms-1 and probably included light. E v B Heinrich Hertz’s Experiment: (proving Maxwell’s theory) Performed in 1886, Hertz built equipment to generate and transmit EM waves with ? ? 1m. He also had a separate receiver (a loop of wire) located about 20m away. Spark gaps were included to show when high voltage AC was present in the transmitter or receiver. The receiver spark only appeared when the transmitter spark was present. Hertz hypothesised that the sparks set up changing electric and magnetic fields that propagated as an electromagnetic ave, as postulated by Maxwell. He showed that these were waves being transmitted because he could reflect, refract and polarise them. By measuring the frequency, he calculated v (v = f ? ) and it came out as 3 x 108 ms-1. These properties proved Maxwell’s theory and as they are also exhibited by light, Hertz was able to provide experimental evidence that light is a form of transverse electromagnetic wave. to induction coil 1mm gap transmitter charged plates re ceiver William Kim HSC Physics Summary | page 37  § Describe Hertz’s observation of the effect of a radio wave on a receiver and the photoelectric effect he produced but failed to investigate Outline applications of the production of electromagnetic waves by oscillating electric charges in radio antennae Hertz observed that the transmitter spark was producing s How to cite Physics Study Notes Hsc, Essay examples

Introduction on Globalization of Music free essay sample

Hip-hop music is funky and is accompanied by a vocal style, which is known as rap along with rhythmic beats. Rap means speaking rhythmically in self-made rhymes with your own style. The term hip-hop music is sometimes used synonymously with the term rap music, because rap is a subpart of hip-hop. Rap and hip-hop are claimed by some to have negative influences on its listeners. The reason for this is that a lot of hip-hop/rap songs contain foul language, messages containing violence and messages where woman are portrayed as sexually devalued objects.While doing research on Globalization and popular music consumption we found it interesting that in particular popular western hip- hop/rap music, is still somewhat unknown and unpopular in the Middle East. We were wondering what contributed to this unawareness or dislike of Western hip-hop/rap. Is it because of the cultural conservatism with many taboos attached or were they just not fond of the music. We will write a custom essay sample on Introduction on Globalization of Music or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page We will take the liberty to elaborate on some of these claims in our research paper by investigating and answering the presented research questions below. Introduction on Globalization of Music free essay sample Most people remember the first time they heard a hip-hop/rap song. No matter where theyre from or what age a person is, they surely have encountered hip-hop/ rap trough several media like; radio, cinema, television, records, cassettes, CDC, live performances and now the internet. Hip-hop/rap came into the existence during the sasss, as part of a cultural lifestyle that started In the late sasss. One of the founding fathers of hip-hoop/rap was Jamaican DC named Clive Campbell known as Cool Here, who Introduced hip-hop music In the Bronx district of New York City.HIP- hop music Is funky and Is accompanied by a vocal style, which Is known as rap along with rhythmic beats. Rap means speaking rhythmically In self-made rhymes with your own style. The term hip-hop music Is sometimes used synonymously with the term rap music, because rap Is a subpart of hip-hop. We will write a custom essay sample on Introduction on Globalization of Music or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Rap and hip-hop are claimed by some to have negative influences on Its listeners. The reason for this Is that a lot of hip-hop/rap songs contain foul language, messages containing violence and messages where woman are portrayed as sexually devalued objects. While doing research on ;Globalization and popular music consumption we found it interesting that in particular popular western hip-hop/rap music, is still somewhat unknown and unpopular in the Middle East. We were wondering what contributed to this unawareness or dislike of Western hip-hop/rap. Is it because of the cultural conservatism with many taboos attached or were they Just not fond of the music. We will take the liberty to elaborate on some of these claims in our research paper by investigating and answering the presented research questions below.

Argumentative Essay on Plastic Surgery

Argumentative Essay on Plastic Surgery Argumentative Essay on Plastic Surgery An earlier article in this document explored the writing of argumentative essays. The present article will rely on the guidelines provided earlier to present a sample argumentative essay on plastic surgery. Beauty has always enjoyed great value in every society, irrespective of the conservative traditions that may prevail in that society. Right from childhood, human beings are taught that a beautiful person always has a prize attached to the beauty. This explains why children exhibit an unconsciousness tendency to describe awesome experiences as being beautiful. In ancient African societies, the embracing of beauty was seen in some communities painting their faces with bright colors. Among the Maasai of Kenya, for example, red ochre was used to paint the face. The trend of appreciating beauty took a different twist as time went by. The Indians pioneered the art of doing nose lifts. It was perceived that women with pointed noses were more appealing to the male generation. Other cu ltures aped this art, and the practice of face lifting and organ firming developed. In the modern world, the term â€Å"plastic surgery† is not new, especially with the rise to fame of the deceased rock musician, Michael Jackson. Recently, plastic surgery has gained substantial recognition among the enlightened generation. Numerous television programs that expose the masses to a hitherto secretive affair boost this. Thanks to plastic surgery, a person can find a lasting solution to certain bodily flaws that are perceived as threatening one’s success in a professional field. The proponents of plastic surgery argue that it greatly assists in enhancing a person’s confidence together with vitality. If you view a typical television show about plastic surgery, you will notice a common principle suggesting that an unhappy individual only needs a surgical operation to turn him or her into a magical success story. However, you have to realize that plastic surgery only bestows temporary confidence. The truth is a cosmetic surgical procedure requires regular maintenance, which means that a series of operations is necessary. Moreover, plastic surgery gives a person unrealistic expectations. He or she goes into the surgical room expecting to come out a transformed individual who will attract others’ positive attention. On the contrary, plastic surgery is a mere illusion in which the person wrongly thinks he/she has acquired more self-esteem. This is gauged by the supposed approval that other people show about the new appearance. Conversely, in most cases, people are driven to seek cosmetic surgery by their spouses or colleagues. It is perfectly understandable to have a desire of remaining youthful. Nevertheless, there are myriad healthy ways of maintaining radiant skin. Instead of opting for a potentially life-threatening superficial operation, why not eat natural foods and exercise regular ly? Besides, there is absolutely no point why you should be moved to such extents by the viewpoints of people who apparently do not value your inner beauty. The true satisfaction in life is achieved when an individual discovers his or her personal identity. Real happiness comes when people embrace their diversities. is committed to provide students with custom argumentative essays about Plastic Surgery. All you need is to place an order at our site!

Should Gov essays

Should Gov essays Should the Gov't Enforce Their Laws Upon its People. To enforce laws upon a society that does not agree with the laws in the first place is not right. A government is there to represent its people not to contradict them. In order to get people to live in a reasonable society, the government has to be open to the peoples' opinions and thoughts on laws that aren't agreed upon. I agree that some laws prevent life from turning into uttermost chaos, however if a large percentage of people do not agree with a certain law that is clearly unreasonable, life will turn into chaos. Its like fighting fire with water. The government being the fire and the the citizens being the water. The government is strong and has a large amount of authority but if they get out of hand the citizens will wash them out. It seems as if the government manipulates peoples' minds. The government forces the "fact" that if there were not certain laws, people would be out of control, which is not necessarily true. An assumption is that people will go out and irresponsibily do things just because there isn't a law on it. So, if the government abolished the law on gun control, everyone would go out and buy guns and kill each other. Or if there were no laws on drugs and dealing drugs, everyone would be addicts. Obviously there is the percentage of people who do go out and do things that are illegal and if the laws were made legal that does not mean that everyone else would go out and do it too. Laws are supposed to keep life and people in order but what about when people break laws. There is the group of people who do go around breaking laws and there are the people who do not. The people who do not break laws live their life according to the limits and borders the government sets for them. The ones who do break laws go beyond the borders and take the risk of getting caught. The thing is when certain people do go out and break laws, and let's ...

My Past, Present, and Future Essay Example | Topics and Well Written Essays - 1000 words

My Past, Present, and Future - Essay Example In order to excel in life one must learn to amalgamate his past with his present so as to have a better future. Remembering the past is a good practice which helps an individual to learn from his mistakes. It is here in this essay that I would put forward my experiences from the past and elaborate as to how these experiences changed my present. Further, everyone has goals in life which they want to attain and my goals would be mentioned here. Beginning from my very early life I learned quite a few things about my family which revolved around the caring nature of my parents. Their caring nature helped me to adjust with many problems of life and it is because of them that I was able to live a life of a normal person. I still remember specific events that took place in my childhood which revolve around my upbringing. This essay would provide all the details about my present, past and future. My Past Present and Future The story of my life begins from my childhood when I was born in a fa mily which belonged to the middle class society. My past is a simple book which revolved around me and my brother who is younger than me. My father belonged to a military background and from the very beginning I saw him in an army dress. It was in my childhood that I developed some interest in the military operations. My parents belonged to two different back grounds. My father was of a African descent whereas my mother was a Hispanic. We lived together as a happy family without facing any sort of family problems. My childhood was a simple one and I only remember specific events that used to take place almost daily in my life. Visiting church was a tradition for our family and I accompanied my parents to the church on every Sunday. My father loved fishing and every now and then he took me to a trip of fishing with him. Altogether I grabbed the skills of fishing through my father who was an excellent fisher. As my father belonged to a military background we had to go through many res huffles in our settlement. We moved through countries after countries because of my father’s transfer in military. It was through these trips that I was able to learn about different cultures. I grasped the skills of diversity and how to handle different situations with different people. My brother at that time did not get along with me well and hence we ended up fighting each other at most instances. However gradually with time we have realized each other’s worth and we love each other till date. Belonging to a middle class family of this sort I never realized the importance of education. If I strived for education at the right moment I could have achieved a better job than I am currently working at. Plato described education in the following strong words â€Å"If a man neglects education, he walks lame to the end of his life† (Freccero & Jacoff 1986) While working in military I still ponder on the words of Plato and wonder if I could rewind my life. As I did n ot pay much heed to studies in life I coped up with the burden of life by adapting to different jobs. In order to cope up with my financial crisis I first worked as a waiter in a fast food restaurant. The experience was not something to be proud of as all day it required work with much less respect in return. The job did not have much returns and I finally decided to leave it to find a better future. It was here that I looked forward to driving for a