**Speed** is equal to distance divided by time. **Velocity** is speed in a particular direction. For the purposes of your question, we can think of speed and velocity as being the same thing.

**Kinetic energy (KE)** is the energy of motion. Any object that is in motion has kinetic energy. Kinetic energy is described by the following equation, where m = mass of the object (kg) and v = velocity:

KE = 1/2 x m x `~v^2`

Therefore, the kinetic energy of an object is proportional to the square of its velocity (speed). In other words,

- If there is a twofold increase in speed, the kinetic energy will increase by a factor of four.
- If there is a threefold increase in speed, the kinetic energy will increase by a factor of nine.
- If there is a fourfold increase in speed, the kinetic energy will increase by a factor of sixteen.

Kinetic energy is related to an object's momentum. For a rigid body traveling in a linear path, kinetic energy increases with the square of velocity. So if the velocity doubles, the kinetic energy quadruples! This relationship partially explains the interesting observation that for a collision of a vehicle going 10 miles per hour with a stationary pedestrian, about 7 people out of 10 will survive the accident; for the same collision with the vehicle going twice as fast, only about 1 person will survive the accident. The vehicle going twice the speed has double the kinetic energy to transmit to the pedestrian!