When a ball rolls down a hill, what energy conversion occurs?

Gravitational potential energy to kinetic energy

Explanation:

For the law of conservation of energy, the total mechanical energy of the ball is constant:

where

is the kinetic energy of the ball, with m being its mass and v its speed

is the gravitational potential energy, with g being the gravitational acceleration and h the height of the ball with respect to the ground

When the ball rolls down a hill, its height above the ground (h) decreases. This means that the gravitational potential energy (U) decreases, but since E (mechanical energy) must remain constant, it means that the kinetic energy (K) increases. Therefore, gravitational potential energy is converted into kinetic energy.