The formula for force is:
F = ma
The formula for the force of gravity is:
Fg = GMm / r ²
G is a constant, M and m are the masses of two bodies, r is the distance between their centers.

Falling Bodies

What is the acceleration of a falling body?

The force acting on a falling body is the force of gravity. For a falling body, we can write:

F = Fg

ma = GMm / r ²
a = GM / r ²


One end of a spring is attached to a wall. The other end of the spring is attached to a block of mass m. The block is on a flat, frictionless surface. The block is pulled out a little distance. This stretches the spring. The block is then released. The stretched spring contracts, pulling the block back to where it started. What is the acceleration of the block?

A restoring force is created in a stretched spring. The formula for restoring force is:

Fr = −kx

The force acting on the block is the restoring force of the spring. We can write:

F = Fr

ma = −kx

a = −kx / m