Isaak Newton

Sir Isaak Newton (1643–1727) was a brilliant English mathema­tician and physicist. It is justly believed that he is one of the great men of science in the history of mankind. __________(1)

Newtonean theory of universal gravitation and his formulation of the basic concepts and principles of mechanics are known as his two great achievements that have made possible the creation of a physical picture of the Universe which remained unshaken until the beginning of the 20th century. It is very important for us to examine, in some details, the concepts he introduced and clarified in the course of his work.__________ (2)

Ever since Galileo had invented his telescope men had been stu­dying the motions of the planets with ever increasing interest and accuracy. In particular, a great deal of observed data had been col­lected by Tycho Brahe, a Danish astronomer (1546–1601). From the­se Kepler deduced his famous three laws describing the motion of the planets about the Sun. They amounted to:

1. The planets describe ellipses, with the Sun being at a focus.

2. The radius vector joining the Sun with the planet describes equal areas in equal times, that is the rate of description of sectorial area is constant.

3. The cubes of the mean distances of the planets from the Sun are proportional to the squares of their times of revolution. _________ (3)

Newton was able to show that these laws were compatible with the assumption that each planet possesses acceleration towards the Sun which is inversely proportional to the square of their distance from it. Furthermore, he believed that this .acceleration was of the same nature as the acceleration of bodies falling near the Earth's .surface. This generalization led him to the concept that all bodies taken in pairs induce in each other mutual acceleration. Translating it into terms of force required a new principle and Newton supplied this principle in his law of "action and reaction" – and this in its turn provides us with a notion of mass not possessed by any of Newton's predecessors. This concept distinguishes between mass and weight. _______ (4)

The laws of motion which Newton published in his "Principia" amount to the following:

Law I. Every body preserves in its state of rest or of uniform motion in a straight line unless it is compelled to alter that state by impressed force.

Law II. Change of momentum is proportional to the impressed force and takes place along the line of action of that force.

Law III. Action and reaction are always equal and opposite; that is to say, the actions of two bodies upon each other are equal and directly opposite._______ (5)

Task 27

True-false test

1. Isaak Newton was a Danish mathema­tician and physicist.

2. Physical picture of the Universe in 18 – 19^th centuries was based on Newtonean discoveries.

3. Telescope was invented by a Danish astronomer.

4. Newton's predecessors were well acquainted with a notion of mass.

5. Newton’s laws were connected with motion.

Task 28

Read the text again and fill in the gaps in the text with the following:

1. Newton stated his 3 laws of motion in his book.

2. Newton's predecessors collected a great deal of observed data.

3. Sir Isaak Newton is an outstanding English scientist.

4. Newtonians concepts were a base for a physical picture of the Universe in those times.

5. Newton got married when he was 40.

6. Newton supplied mankind with a notion of mass not possessed by any of his predecessors.

Enjoy yourself!