You know that when you throw a ball up in the sky, it will go up but will ultimately come back to earth. The same applies to everything that falls down from a height whether an apple from a tree or a paper ball thrown by a boy from his balcony. Have you ever wondered why does this happen all the time? Well, Sir Isaac Newton (1642-1727) certainly wondered about the fact when an apple from a tree fell down while he was lying down on the ground.

- He was the first to talk about the force of gravity that makes an apple fall from the tree.
- He also explained how humans and animals lived on earth without falling off despite the planet revolving around the Sun.

**Gravity as Explained by Newton**

People only speculated about gravity before Newton. He was the first man to describe the Universal Law of Gravitation. His theory helped explain falling of objects back to the surface of the earth and also how the planets continue to revolve around the Sun, the center of our solar system.

It is hard to describe or define gravity. In fact, gravity is a force of attraction that exists between any two bodies in our universe. It can only be described as an area of influence of an object or a body it was Newton who discovered that it is this force of gravity that is required to change the direction and velocity of a moving object.

**Mathematical Equation Involving Gravity**

If one talks about the force of attraction between two bodies, he finds that this force of gravity is proportional to the product of the masses of the two bodies and inversely proportional to the square of the distance between their centers of mass. This is a mathematical equation that can be shown as

**F = G M1 M2/ rXr**

**Some Interesting Facts about Gravity**

Here, G is a constant called gravitational constant. The value of G is strongest at the surface of the body and it extends in all directions up to infinity.

- Gravitational force or attraction reduces with distance and its strength goes down as one move away from the surface or the body of the object.
- One interesting fact about gravity is that we are stuck to earth because of its gravity but we are also pulled back by Sun towards it through its gravity. However, we never feel this gravitational pull as it is very minute at the surface of the earth.
- It is this gravitational pull of the earth that keeps the earth rotating around it all the time.
- We never feel the pull that moon exerts on us though the oceanic tides are a result of this gravitational pull exerted by the moon only.

The principle of gravity was later picked up by Albert Einstein to come up with his theory of relativity. Despite path breaking research by these two scientists, our understanding of gravity is still not complete and it is hard to explain gravity at the most basic level.

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