Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

KE compared to mass equivalent at low speeds

An object is moving at ordinary nonrelativistic speeds. Compare its kinetic energy to the energy mc2 it has purely because of its mass.

The speed of light is a very big number, so mc2 is a huge number of joules. The object has a gigantic amount of energy because of its mass, and only a relatively small amount of additional kinetic energy because of its motion.

Another way of seeing this is that at low speeds, γ is only a tiny bit greater than 1, so E is only a tiny bit greater than mc2.

Last Update: 2010-11-11