A Brief History of Ideas About Forces
In about 350 BC the Greek philosopher Aristotle stated without proof fall faster than light objects. Aristotle also believed that objects will only continue to move as long as forces act on them. To many people this appears to be true because because friction is a hidden force than many people ignore.
It wasn't until Galileo did some experiments in motion and moving bodies that real advances were made. In 1589 he investigated balls rolling down an inclined plane. He showed that forces cause a change in an objects motion. In practice this force is often friction, often appearing as air resistance, as when an object is thrown through the air. Galileo demonstrated Aristotle to be wrong in thinking that heavier objects fall faster by dropping balls of different weight from the top of the leaning tower of Pisa. Both objects hit the ground at the same time.
Robert Hooke showed in 1657 that a feather and a coin fall at the same rate in a vacuum.
It was Isaac Newton though that caused a revolution in physics iby putting forward a comprehensive theory of forces and motion, in 1687, so that all things on Earth and in Heavan moved according to the same laws of physics. He showed that all changes in motion were caused by unbalanced forces acting on a body, and expressed acceleration in terms of these with the equation
Newton's ideas seemed to work perfectly, and contributed greatly to the industrial revolution in Britain. It wasn't until Einstein published his theories of relativity in 1905 and 1916 that Newton's theories had to be modified. Even then, they work so well that they are used to calculate orbits of satellites and routes for spacecraft. Einstein showed that the presence of matter and energy curved space and time. Light continues to travel in straight lines through space, but because space is curved, so effectively is the path followed by light. Other strange predictions of Einstein's theories are that the mass of a moving body increases as the speed of light is approached, and that it is possible for spacetime to be so curved as to close in on itself, creating a 'black hole' from which nothing can escape.