⚡ Kinetic Energy Calculator
Calculate KE = ½mv² from mass and velocity.
Result
How to Use This Calculator
This calculator finds the kinetic energy of a moving object from its mass and velocity. Enter both values and the energy appears in joules instantly.
Enter the mass in kilograms.
Enter the velocity in meters per second. Direction does not matter, only speed.
Click Calculate, or keep typing. The result updates live.
Read the kinetic energy in joules. Large values are also shown in kilojoules.
The Kinetic Energy Formula
Kinetic energy is the energy of motion: the work it would take to bring the object to rest, or equivalently the work that was done to get it moving. The 1/2 and the square come from integrating force over distance. The practical consequence is dramatic: at highway speeds, a car's energy is dominated by velocity, not mass. A small car going fast carries more destructive energy than a heavy truck crawling slowly.
Energy is a scalar, so unlike momentum it has no direction. Two cars of equal mass approaching each other at the same speed have opposite momenta that cancel, but their kinetic energies add. That is why head-on collisions are so violent: the total energy that must be absorbed is the sum, not the difference.
Worked Example
Where This Comes Up
Crash safety engineering is applied kinetic energy. Crumple zones, airbags, and guardrails all exist to dissipate a car's KE over a longer distance, which lowers the peak force. Sports science uses it too: a 160 km/h tennis serve carries about 56 J, and bat or racket design is about transferring KE efficiently. Flywheels store grid energy as rotational kinetic energy, the spinning cousin of this formula.
Unit slips are the usual failure. Velocity must be in m/s: 100 km/h is 27.8 m/s, and entering 100 directly inflates the answer by a factor of 13. Also remember that only speed counts. A satellite in a circular orbit has huge kinetic energy even though its velocity direction constantly changes.
Frequently Asked Questions
Why is velocity squared in the formula?
It comes from the work-energy theorem: pushing a mass with constant force over distance d does work Fd = mad, and substituting v^2 = 2ad gives 1/2mv^2. The square means speed matters far more than mass.
What are the units of kinetic energy?
Joules (J). One joule is one newton-meter: the energy of a 2 kg mass moving at 1 m/s is exactly 1 J.
Can kinetic energy be negative?
No. Mass is positive and velocity is squared, so kinetic energy is always zero or positive. Direction of motion does not matter.
What is the work-energy theorem?
The net work done on an object equals its change in kinetic energy. Brakes do negative work on a car, removing kinetic energy until it stops.
How does kinetic energy relate to braking distance?
Stopping means dissipating all kinetic energy as heat in the brakes. Since KE grows with v^2, doubling your speed quadruples the braking distance, assuming the same braking force.