01-04-2020-Дедушенко И.С.Обучение чтению и устной речи на английском языке (1171845), страница 2
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Thereis an attraction between the two magnets, causing the reading onthe top scale to increase and the reading on the bottom scale todecrease. The large magnet is more “powerful” in the sense that itcan pick up a heavier paperclip from the same distance, so manypeople have a strong expectation that one scale’s reading willchange by a far different amount than the other.
Instead, the twochanges are found to be equal in magnitude but opposite indirection: the force of the bottom magnet pulling down on the topone has the same strength as the force of the top one pulling upon the bottom one.In the second experiment, two people pull on two springscales. Regardless of who tries to pull harder, the two forces asmeasured on the spring scales are equal. Interposing the twospring scales is necessary in order to measure the forces, but theoutcome is not some artificial result of the scales’ interactionswith each other.
If one person slaps another hard on the hand, theslapper’s hand hurts just as much as the slappee’s, and it doesn’tmatter if the recipient of the slap tries to be inactive. (Punchingsomeone in the mouth causes just as much force on the fist as onthe lips. It’s just that the lips are more delicate. The forces areequal, but not the levels of pain and injury.)Newton, after observing a series of results such as these,decided that there must be a fundamental law of nature at work:Newton’s third law: Forces occur in equal and oppositepairs: whenever object A exerts a force on object B, object Bmust also be exerting a force on object A.
The two forces areequal in magnitude and opposite in direction.In one-dimensional situations, we can use plus and minussigns to indicate the directions of forces, and Newton’s third lawcan be written succinctly as FA on B = –FB on A.There is no cause and effect relationship between the twoforces. There is no “original” force, and neither one is a responseto the other. The pair of forces is a relationship. Newton came upwith the third law as a generalization about all the types of forces9with which he was familiar, such as frictional and gravitationalforces. When later physicists discovered a new type force, such asthe force that holds atomic nuclei together, they had to checkwhether it obeyed Newton’s third law. So far, no violation of thethird law has ever been discovered, whereas the first and secondlaws were shown to have limitations by Einstein and the pioneersof atomic physics.Newton’s third law does not mean that forces always cancelout so that nothing can ever move.
If the two figure skaters,initially at rest, push against each other, they will both move.It often sounds as though Newton’s third law implies nothingcould ever change its motion, since the two equal and oppositeforces would always cancel. The two forces, however, are alwayson two different objects, so it doesn’t make sense to add them inthe first place — we only add forces that are acting on the sameobject. If two objects are interacting via a force and no otherforces are involved, then both objects will accelerate — inopposite directions!It doesn’t make sense to refer to the equal and opposite forcesof Newton’s third law as canceling. It only makes sense to add upforces that are acting on the same object, whereas two forcesrelated to each other by Newton’s third law are always acting ontwo different objects.Newton’s third law is completely symmetric in the sense thatneither force constitutes a delayed response to the other.Newton’s third law does not even mention time, and the forcesare supposed to agree at any given instant.
This creates aninteresting situation when it comes to non contact forces. Supposetwo people are holding magnets, and when one person waves orwiggles her magnet, the other person feels an effect on his. In thisway they can send signals to each other from opposite sides of awall, and if Newton’s third law is correct, it would seem that thesignals are transmitted instantly, with no time lag.
The signals areindeed transmitted quite quickly, but experiments withelectronically controlled magnets show that the signals do not10leap the gap instantly: they travel at the same speed as light,which is an extremely high speed but not an infinite one.Is this a contradiction to Newton’s third law? Not really.According to current theories, there are no true non contactforces. Action at a distance does not exist.
Although it appearsthat the wiggling of one magnet affects the other with no needfor anything to be in contact with anything, what really happensis that wiggling a magnet unleashes a shower of tiny particlescalled photons. The magnet shoves the photons out with a kick,and receives a kick in return, in strict obedience to Newton’sthird law. The photons fly out in all directions, and the ones thathit the other magnet then interact with it, again obeyingNewton’s third law.Light is made of photons, but our eyes receive such hugenumbers of photons that we do not perceive them individually.The photons you would make by wiggling a magnet with yourhand would be of a “color” that you cannot see, far off the redend of the rainbow.(5366)Discussion1.
Show that the Newton can be reexpressed in terms of thethree basic mks units as the combination kgm/s2.2. What is wrong with the following statements?(1) “g is the force of gravity.”(2) “Mass is a measure of how much space something takes up.”3. Criticize the following incorrect statement:“If an object is at rest and the total force on it is zero, it staysat rest. There can also be cases where an object is moving andkeeps on moving without having any total force on it, but that canonly happen when there’s no friction, like in outer space.”4.
Newton said that objects continue moving if no forces areacting on them, but his predecessor Aristotle said that a force wasnecessary to keep an object moving. Why does Aristotle’s theory11seem more plausible, even though we now believe it to be wrong?What insight was Aristotle missing about the reason why thingsseem to slow down naturally?5. Interpret the equation vterminal = 0.6. How would the terminal velocity of a 4-cm steel ballcompare to that of a 1-cm ball?7.
Criticize the following incorrect statement: “If you shove abook across a table, friction takes away more and more of itsforce, until finally it stops”.8. You hit a tennis ball against a wall. Explain any and allincorrect ideas in the following description of the physicsinvolved: “The ball gets some force from you when you hit it,and when it hits the wall, it loses part of that force, so it doesn’tbounce back as fast. The muscles in your arm are the only thingsthat a force can come from”.Grammar revisionEx.
1. Express the idea using the verbs in brackets.Model: This value increases. (assume) — The value isassumed to increase.1. These data are in good agreement with the experimentalones. (consider).2. Density changes with temperature. (know)3. The distance is shown indirectly. (expect)4.
The altitude is uniform during this period of time. (seem)5. The value is derived from the above equation. (suppose)6. The path is reduced twice. (appear)7. The photons fly out in all directions. (believe)8. The first and second laws have limitations. (show)Ex. 2. Translate into Russian paying attention to ComplexSubject with the Infinitive.1. An object initially at rest is predicted to remain at rest if thetotal force on it is zero.122. Both forces are known to continue to exist because theyboth have side-effects.3. Pressure is known to act equally in all directions.4. When the car gets going down decreased force is needed tospeed it up.5. The predicted precision was found to be difficult to obtainin practice.6.
Everyone seems to realize the potential dangers of somescientific discoveries.7. An object initially at rest is predicted to remain at rest if thetotal force on it is zero.8. The property appears to have been mentioned frequently inthe past.9. The information is assumed to provide an appropriatesolution to the problem.Ex.
3. Translate into Russian, paying attention to thefunction of the infinitive in the sentence.1. Acceleration of an object is shown to be directlyproportional to the total force applied to it.2. To introduce numerical methods and their use in physics isthe purpose of this paper.3. Acceleration is said to be inversely proportional to theobjects mass.4.
The methods to be introduced are extremely useful forsolving many practical problems.5. To come to this conclusion we have exerted much in thisfield.6. We have nonnegligible evidence to predict this result.7. The set of laws to be involved in these calculations must bestudied in detail.8. To interpret these results in terms of your concept is ratherdifficult.139. Two forces to act on the feather are a downwardgravitational force from the planet earth, and an upward frictionalforce from the air.10.
In that case air force was said to be negligible.Ex. 4. Translate into English, using different forms of theinfinitive.1. Вот движение тела, которое нужно объяснить.2. Для того чтобы объяснить движение тела, мывовлекаем понятие инерции.3. Уравнение, которое необходимо решить в данномслучае, требует длительных вычислений.4. Для того чтобы облегчить наши вычисления, мывоспользуемся компьютером.5.
Для того чтобы предсказать конечный результат, мывовлекаем знакомые нам понятия.6. Применить эти понятия к данным явлениям — цельнашей работы.14Unit 2. CONSERVATION OF ENERGYMemorize the following vocabulary to text 2A.collide v — сталкиватьсяcollision n — столкновениеfail v — не суметь, не быть в состоянии, оказатьсянеспособнымturn smth into smth — превращать что-то во что-тоsubstance n — веществоperpetual motion — постоянное движениеexert v — напрягать силы, прилагать усилияencounter v — сталкиваться, встретитьсяlay odds — давать преимуществоText 2A.
The Search for a Perpetual Motion MachineRead, translate and render the text.Don’t underestimate greed and laziness as forces for progress.Modern chemistry was born from the collision of lust for goldwith distaste for the hard work of finding it and digging it up.Failed efforts by generations of alchemists to turn lead into goldled finally to the conclusion that it could not be done: certainsubstances, the chemical elements, are fundamental, and chemicalreactions can neither increase nor decrease the amount of anelement such as gold.Now flash forward to the early industrial age. Greed andlaziness have created the factory, the train, and the ocean liner,but in each of these is a boiler room where someone gets sweaty15shoveling the coal to fuel the steam engine.
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