Why does an object accelerate when falling to earth's surface?

The reason behind the acceleration of free falling objects to earth's surface is Gravity. This is a force which acts on any and everything that is present on the surface of the earth. It pulls everything to the earth. It is also known as gravitational pull. Any object that is thrown into the air falls back done to the surface because of gravity. The velocity of any such free falling object is calculated to be 9.8 m/s², which is rounded off to 10m/s² for convenience.