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Kinetic Energy

Kinetic energy is energy due to the motion of an object.

  • A track and field runner has kinetic energy.
  • A ballet dancer leaping through the air has kinetic energy and potential energy.

two runners running on a track and a ballerina jumping through the air

The kinetic energy of an object depends on the massamount of matter; usually measured in kg and speedhow fast an object is going; usually measured m/s of the object.

The equation for kinetic energy is:

KE = 1/2 mv2

In this formula:

  • KE stands for kinetic energy
  • m equals mass
  • v equals velocity

The unit of measurement for energy is a joule (J), which is kg·m2/s2. We use the joule as the unit of measurement for all types and forms of energy, including kinetic energy and potential energy.

Look at the equation carefully to determine what the relationship is between kinetic energy, mass, and velocity.

What happens to kinetic energy as mass increases?

What happens to kinetic energy as velocity increases?

Example Problem

What is the kinetic energy of a 2000 kg car moving at a velocity of 15 m/s?

Remember, first list what you are given in the problem.

m = 2000kg

v = 15 m/s

KE = ?

Then plug in your values and solve.

KE = ½ (2000kg) (15m/s)2

The kinetic energy of this car is 225,000 J.

Watch GPB Segment E: Kinetic Energy and Gravitational Potential Energy (5:14) to learn more.

Then, read the Kinetic Energy page from The Physics Classroom and complete the four Check Your Understanding questions at the bottom of the page.