Why does an object accelerate when it falls toward earth surface?

Because the constant force of gravity is acting on it, and the acceleration of an object is equal to( net force acting on the object) divided by( the objects mass).

Because of the earth gravity. gravity is one of things that holds us down and if u have something like say i have a basketball and u drop it off of a 10 story building its going to fall at a rate that is faster then 10 mph. so ur answer would be gravity  

i hope this helps u XD plz tell me if i'm wrong