# Sir Issac Newton

Isaac Newton

Newton was born on the 25th December 1642 and died in 1727. He was born

In Woolsthorpe in Lincolnshire. His father was a farmer but he died

Three months before Newton was born. His mother remarried and Newton

spent his childhood with his grandmother. At school he showed great

skill in making model kites, sundials and windmills. In 1665 when he was

18 he went to study mathematics at Cambridge University. He continued

his studies at home when the University closed because of the plague.

The Reflecting Telescope

Because Newton was working with light in 1668 he made the first

reflecting telescope. The light was collected and reflected from a

curved mirror instead of being refracted through a lens. It was far

superior from the refracting telescopes at that time because it

reflected all the light in the same way. It did not produce colour

fringing or blurring which occurred in the early refracting telescopes.

The Nature of Light

Newton discovered the nature of light when he darkened his room and

"made a small hole in my shuts to let in a convenient quantity of the

sun's light." He passed this beam of sunlight through a prism. When the

light came out of the prism is was not white but was of seven different

colours: Red, Orange, Yellow, Green, Blue, Indigo and Violet. The

spreading into rays was called DISPERSION by Newton and he called the

different coloured rays the SPECTRUM. He learnt that when the light rays

were passed again through a prism the rays turned back into white light.

If only one ray was passed through the prism it would come out the same

colour as it went in. Newton concluded that white light was made up of

seven different coloured rays. The rays were dispersed through the prism

because the rays were reflected at different angles.

Newton wondered whether the different colours of the spectrum travelled

at different speeds. He wrote to Flamstead to ask if when he observed an

eclipse whether the colour changed all at once of at different times.

Flamstead wrote back to him to say that the colours changed all at once.

The Calculus

Newton invented the Calculus branch of mathematics around 1669. He did

not publish his ideas until around 1704, 35 years later. This branch of

mathematics is divided into two parts:

Differential Calculus

Integral Calculus

Differential Calculus

Differential Calculus deals with the rates things change at. When a car

moves off from a halt the distance changes slowly at first. When the

speed increases the distance changes quicker. As shown in the graph

below:

What really happens is shown below:

The car accelerates quickly at first. The acceleration drops as the car

changes gear. The acceleration is zero when the car reaches a cruising

speed. Differential Calculus is used to calculate the orbits of planets

and satellites very exactly.

Integral Calculus

Integral calculus is used for measuring quantities by dividing them into

many small parts. An example is the area of a circle. The circle is

divided into sectors. As the number of sectors increases the size of the

sectors get smaller. The sectors are arranged into a rectangle:

As the sectors shrink to almost nothing, the shape is almost a

rectangle. The height of the rectangle is almost equal to R (Radius) and

the width is ?C (Circumference), as the circumference is spread between

the bottom and top of the rectangle. The area of the rectangle is R x ?C

. As C=2pR the area of the rectangle is R x ? 2pR or pR2.

The books Newton wrote

Newton's most famous book was called "Philosphe Naturalis Principia

Mathematica" It was published in 1678 and was known as "Principia". The

book contains all his laws of motion and theories of tides and

gravitation. He also wrote another book, "Optiks", which was published

in 1704 and describes the Calculus and other mathematics. It also

describes his theory of light.

Motion and Gravity

In 1670 Newton worked more on chemistry and alchemy than on optics and

mathematics. It is said that Newton wondered why objects fell to earth

when he was sitting in a garden and saw an apple drop in front of him.

This is still believed by some people although many people think it is

untrue. Newton thought back to the subject which he was thinking about

in 1665-66. This was "Why things move as they do." He made three laws of

motion:

First Law of Motion

A body continues in a state of rest or to move with a steady velocity in

a straight line if it is not acted upon by forces.

If a ball is kicked in outer space it will continue to move at the same

speed as no forces act upon it, such as friction and air resistance.

If a ball is kicked on earth it will slowly come to halt on the ground

as friction, air resistance and gravity have acted upon it.

Second Law of Motion

When a force acts on body it produces an acceleration which is

proportional to the magnitude of the force.

If a ball is kicked its acceleration is related to the power of the kick

and the mass of the ball. The ball also moves in the direction of the

force. Therefore a small, light ball travels faster than a big, heavy

ball.

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