This calculator finds the kinetic energy of a moving object from its mass and speed. Enter the values and it returns the energy of motion in joules and other units.
What the symbols mean
- E — kinetic energy (joules).
- m — mass of the object (kilograms).
- v — speed of the object (metres per second).
Worked example
A 1,500 kg car at 20 m/s has a kinetic energy of ½ × 1500 × 20² = 300,000 J. Double the speed to 40 m/s and the energy quadruples to 1.2 MJ — because speed is squared.
Want the full story behind this formula? Read our guide: Kinetic Energy.
How the formula works
Kinetic energy is the energy an object has because it is moving. The formula comes from calculating the work needed to accelerate an object from rest to its speed. Because the distance covered grows as the object speeds up, summing those contributions produces the factor of one-half and the velocity squared.
The squared velocity is the formula's most important feature: it means speed matters far more than mass. Doubling an object's speed quadruples its kinetic energy, while doubling its mass only doubles it.
Common mistakes to avoid
- Forgetting the one-half. It is essential and comes directly from the derivation.
- Not squaring the velocity. Only v is squared, not the mass.
- Using speed in km/h. Convert to metres per second first, or use the unit selector.
Where it is used
Kinetic energy underlies vehicle stopping distances, the destructive energy of impacts, the design of roller coasters, wind-turbine output, and countless problems where motion converts to and from other forms of energy.