NEWTON'S THREE LAWS OF MOTION
Isaak Newton was born in 1642 in England. Isaak attended1 a country school until he was eleven. At the age of twelve he was sent to a town school, seven miles away from his home, to continue his education. The boy made good progress2 and worked hard for his goal – Cambridge. His application3 for entrance into Cambridge University was accepted4 in 1661.
Soon his tutors found that he showed unusual knowledge of subjects that were to form the topics of further lectures. He had mastered5 those subjects independently because he was interested in them. The result was that he was soon excused from attending certain courses, which provided him with more time for making experiments.
Newton's interests were centred on mathematics and mechanics and on studying different phenomena of Nature. Newton was forty-two years old, however, when he started putting down on paper his ideas which were the result of more than twenty years of scientific thinking. It is indeed surprising that it took Newton only eighteen months to produce his wonderful work — the Principia, that was later on called the greatest product of a single human mind.
Of the many things that Newton accomplished6 in the Principia, the major ones, namely the three laws of mechanics, are briefly touched upon below.
First Law. Every body continues in its state of rest or uniform motion in a straight line except in so far as it may be compelled by impressed force to change that state.
The first law introduces the idea of inertia and is often called the low of inertia. Inertia is defined7 as that property by virtue of which a body resists-changes, in motion.
Suppose that you are riding in a bus going 20 miles per hour. The bus stops suddenly. It is no longer doing 20 miles per hour. But you are. Unless you seize a handrail, you will keep moving due to your being a "body" in motion. Your having experienced a thrust is a demonstration of inertia.
On the Earth's surface, however, it is difficult to demonstrate8 fully the first law of motion because air-resistance9 and the tremendous forces of gravity prevent an object from travelling at constant speed in a straight line. But one of the first proofs of the first law is found in the movement of the heavenly bodies which meet practically no friction in their travelling through space.
Modern artificial satellites obey Newton's first law. Their being set on proper orbits, completely free from the Earth's atmosphere and air friction, is of great importance. It is known that some early satellites were burned up on account of their having been set on wrong orbits. Successful flights of modern spaceships have proved the validity of Newton's first law in actual practice.
Second Law. Any change in motion of a body is in proportion to the force pressing on it and takes place in the direction of the straight line in which the pressing force acts.
The second law gives a valuable means for measuring forces. The mathematical relationships provided by the second law allow scientists to measure the force of gravitation at any point of the Earth's surface. The ability of making such calculations10 is of great value in planning the orbit of an artificial satellite. The availability of electronic computers provides a reliable means for making the necessary calculations with great speed and accuracy.
Third Law. For every action exerted11 on a body, there is an equal and opposite reaction12. Another way of stating the third law is this: "Whenever one body exerts a force on another, the second body exerts an equal and opposite force on the first body."
For example, when you press a stone with your finger, your finger is also pressed back by the stone.
When you fire a rifle, the forward thrust of the bullet is matched13 by a backward thrust or "kick" against your shoulder.
Nowhere else today, perhaps, is Newton's third law of motion of such great importance as in the field of jet propulsion and rocket flights.
In the case of jet-propelled plane's flying the thrust of gases issuing from the jet engine reacts against the engine itself and causes a forward thrust. It is not true, as it was thought before, that the rearward gases push against the air; if it were so, Newton's third law would not be true. But jet engines are air-breathers and the hot gases burned in them feed on the air supply14 they take from the atmosphere.
Rockets, on the other hand, carry their fuel15 along with them and are able of travelling in outer space where there is no air and, hence, no air resistance. In the near-perfect vacuum of space Newton's third law operates ideally. The powerful thrust inside the rocket's engine results in an equal and opposite thrust forward of the rocket itself because there is no air-friction in outer space. Hence, the rockets' travelling with fantastic speeds of thousands of miles per hour is possible.
Both in the world of science and in our own daily lives Newton's three brief statements of motion are of great importance. In his three laws of motion Newton established16 the framework for the general study of motion in terms of mass and force.
The greatest achievements17 of science and engineering today are based18 on Newton's laws of motion, which are always and everywhere true.
Примечания к тексту:
are briefly touched upon below – вкратце даны ниже;
When you fire a rifle – когда вы стреляете из винтовки;
impressed force – приложенная сила;
in proportion – пропорционально;
on account of – вследствие, из-за, благодаря;
by virtue of – вследствие;
air-breather – воздушно-реактивный двигатель;
to push against smth. – отталкиваться от чего-л., опираться на что-л.