# Where does an object get kinetic energy?

Where does an object "obtain" kinetic energy? I understand that an object often gets kinetic energy from another object. Where does the first object get the energy?

• One example is from potential energy: $E_p = mgh$ – Ruben Feb 12 '14 at 4:22

Where does an object "obtain" kinetic energy?

Ruben is correct. An object can convert it's potential energy into kinetic energy. For example see the below figure, where potential energy of water has been converted into kinetic energy.

A moving body can transfer some of its energy to set another body into motion. For example, when a billiard ball collides with another billiard ball, it sets it into motion.

I understand that an object often gets kinetic energy from another object

This may not be always true, for example in the example given above. Water converts it's potential energy into kinetic energy.

Where does the first object get the energy?

Einstein showed from his theory of relativity that it is necessary to treat mass as another form of energy. So, object what you are speaking about is nothing but energy (mass).