Almost 300 years after his death, Sir Isaac Newton is still a household name thanks to his ground-breaking theories on gravity and motion which explain the movement of most objects under everyday conditions
ALMOST 300 years after his death, Sir Isaac Newton is still a household name thanks to his ground-breaking theories on gravity and motion which explain the movement of most objects under everyday conditions.
Newton (1642–1727), born in a tiny Lincolnshire village, was the best-known physicist and mathematician of his day.
He began his university education in 1661 at Trinity College, Cambridge, when the ancient ideas of the Greek philosopher Aristotle (384– 322 BC) still held sway.
Some scientists had begun to overturn those long-standing notions.
By the time Newton went to college, many were convinced matter was made of tiny particles and that Earth and other planets orbit the sun – the ‘heliocentric’ theory.
Newton learned about these ideas and filled his notebooks with ‘philosophical questions’, which he would follow up later.
In 1665, the university was closed for 18 months when plague broke out in London.
Newton went to stay at his mother’s house in Lincolnshire and there, still in his mid-20s, he made most of his important discoveries.
In a darkened room, Newton passed sunlight through glass prisms and lenses.
For hundreds of years, people had seen the result of this – a spectrum of all the colours of the rainbow – but everyone assumed they were added by the prism.
Newton said the colours are within the light.
He analysed light in a series of classic experiments, laying down firm foundations for modern optics, the study of light.
It is said that while doing this he invented the cat flap to avoid being disturbed by his pet’s comings and goings.
There is no proof of this story – but it has been in circulation for decades.
Another, more likely, story is that Newton had his famous revelation about gravity while sitting under an apple tree at his mother's house.
He realised that the same force of gravity that causes apples to fall to the ground applies at much greater distances.
He realised it also pulled the moon towards Earth, keeping it in our orbit.
By extending the same argument to the sun and the planets, Newton could see that gravity was a universal force responsible for keeping planets in their orbits, backing the heliocentric theory.
They are simple, but not obvious.
For example, the first law says a moving object will carry on moving forever unless a force acts on it.
That is not our experience of everyday life – but only because friction is the force that slows objects down.
Aristotle had wrongly said things stop moving unless there is a force to keep them moving, which is the common sense view.
Newton’s second law says that the rate a moving body speeds up or down is proportional to the force acting on it.
The third law says that for every ‘action’ – or force applied to a body – there is an equal and opposite reaction.
He published his discoveries about motion and gravity in 1687, in perhaps the most important scientific book of all time: Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy).
It brought him great acclaim in Britain and across Europe.
His second most important book, Opticks, was published in 1704; it contained his discoveries about light.