Kinetic energy is the energy that an object has by virtue of its motion. It is given by the formula:
kinetic energy = ½ m v2
where m is the mass of the object and v is its velocity.

In the SI (metric) system of units:
• m is expressed in kg (kilograms),
• v is expressed in m/s (meters per second),
• the energy is expressed in J (joules).

Note that if the velocity of an object is doubled, its kinetic energy is quadrupled.

Kinetic energy can also can be converted into other forms of energy. For example on mountain roads runaway lanes are often provided for trucks that lose their brakes while going down long hills. The runaway lane takes the truck back uphill and allows the truck to coast to a stop as its kinetic energy is converted to potential energy.