Question: what is gravity?

Kuntal Singh answered on 15 Nov 2016:

Gravity is a force that causes all matter to be attracted to all other matter. Gravity is responsible for making an apple fall to the ground. When an apple falls, both the apple and the ground are attracting each other, however ground have more mass and therefore a stronger gravitational pull and hence apple goes down rather than ground going up.

It is the same reason why all planets revolve around the sun because sun’s gravity pulls them towards it. You may ask than why planets don’t fall inside the sun. The reason is that planets are moving sideways. For e.g. (I borrowed this example from the internet) if you swing around a weight at the end of a string, the weight is being pulled towards you but at the same time the movement of the weight is sideways. That’s why the planets don’t fall into the sun. They are moving sideways but do not escape their orbit because sun’s gravity keeps them in place.