Kinetic energy is the energy an object has because it is moving. This works it out from mass and velocity, and shows why speed matters far more than mass does to the result.
Key terms
- Mass — how much matter the object has, in kilograms.
- Velocity — speed in a direction, in metres per second.
- Kinetic energy — the energy of motion, in joules.
How it works
Kinetic energy
KE = ½ m v²
m is mass in kilograms, v is velocity in metres per second, KE comes out in joules.
Why velocity matters so much more than mass
Mass enters the formula in direct proportion — double the mass, double the energy. Velocity is squared — double the velocity, and the energy multiplies by four, not two. This is the entire reason a car’s stopping distance grows so sharply with speed: the energy the brakes have to dissipate as heat has grown by the square of the speed increase, which is why a crash at twice the speed is not twice as severe — it is four times the energy that has to go somewhere.
How to use this calculator
- Enter the mass in kilograms.
- Enter the velocity in metres per second.
- Read the energy in joules, or the more convenient kilojoules for larger figures.
Frequently asked questions
Why is velocity squared in the formula?
It comes directly from integrating force over distance for an object accelerating from rest — the mathematics of that derivation is what produces the square, not an arbitrary choice. The physical consequence is that speed dominates kinetic energy far more than mass does.
Does direction matter for kinetic energy?
No — kinetic energy only depends on speed, the magnitude of velocity, not its direction. Two identical cars moving at the same speed in opposite directions have identical kinetic energy, even though their momentum (a different quantity) points opposite ways.
What happens to kinetic energy when something stops?
It converts to other forms — heat in brakes and tyres, sound, deformation of materials in a crash. Energy is not destroyed, only converted, which is the underlying reason a sudden stop at speed is dangerous: a large amount of energy has to go somewhere very quickly.
Why does a small increase in speed matter so much in a crash?
Because of the squaring: a 10% increase in speed is a 21% increase in kinetic energy, not 10%. This is part of why speed limits are set where they are — the energy involved in a collision rises much faster than the speed itself.
Is this the same energy the potential energy calculator computes?
Related, not identical. An object falling converts potential energy into kinetic energy as it speeds up — the potential-energy calculator on this site computes the first quantity, this one the second, and for a simple drop (ignoring air resistance) the two match exactly at the moment of landing.
