Calculate the kinetic energy of a moving object from its mass and speed. Choose kilograms or pounds and your speed unit, and see the energy in joules, kilojoules and foot-pounds. Free, private, and runs entirely in your browser.
Kinetic energy is half the mass times the square of the speed. Because speed is squared, doubling the speed quadruples the energy.
Why does speed matter so much? Because energy grows with the square of speed. A car at 100 km/h has four times the kinetic energy of the same car at 50 km/h.
What are the units? Joules when the mass is in kilograms and the speed in meters per second.
A 1,000 kg car moves at 20 m/s (72 km/h). KE = 0.5 × 1,000 × 20² = 200,000 J = 200 kJ, which is about 147,500 ft-lbf.
How does kinetic energy relate to stopping distance? For a constant braking force, the energy to remove equals force times distance, so distance grows with the square of speed.
What is the energy of a bullet? It depends on mass and speed. A 4 g bullet at 400 m/s carries about 320 J.
Gottfried Leibniz studied the quantity he called vis viva, proportional to mass times speed squared, in the 1680s. Gaspard-Gustave Coriolis introduced the factor of one half in 1829, and the term kinetic energy came into use in the mid-19th century, associated with William Thomson, later Lord Kelvin.
Use this calculator for physics problems, vehicle safety comparisons and sports science. A 70 kg person running at 5 m/s has 875 J of kinetic energy. For the path of a thrown object, see the projectile motion calculator.
How do I convert joules to foot-pounds? Multiply joules by 0.7376.
What is the difference between kinetic and potential energy? Kinetic energy is energy of motion, and potential energy is stored energy due to position, such as height.