What is the kinetic energy formula?

KE = ½mv², where m is mass in kilograms and v is velocity in metres per second. The result is in joules.

Why does doubling speed quadruple energy?

Because velocity is squared in the formula. Twice the speed is four times the energy, which is why stopping distances and crash severity rise so much faster than speed does.

What is the difference between kinetic energy and momentum?

Momentum is mv and scales linearly; kinetic energy is ½mv² and scales with the square. Momentum is conserved in a collision, kinetic energy usually is not — the difference becomes deformation, heat and sound.

How much energy does a car have at motorway speed?

A 1,500 kg car at 70 mph, about 31 m/s, carries roughly 720 kilojoules — comparable to the energy of a stick of dynamite. All of it has to go somewhere in a crash.

Why do speed limits matter so much near schools?

Because the energy a pedestrian absorbs scales with the square of the impact speed. The difference between 20 and 30 mph is more than double the energy, and survival rates reflect that.

Kinetic Energy Calculator

Solve KE = ½mv² for energy, mass or velocity, with everyday comparisons.

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About the Kinetic Energy Calculator

Kinetic energy is ½mv², and the square on velocity is the whole story. Doubling the speed of a car quadruples its kinetic energy — which is why stopping distances grow so much faster than speed, and why a crash at 60 mph is four times as violent as one at 30, not twice.

Momentum, by contrast, is mv and scales linearly. The two behave differently in collisions: momentum is conserved, kinetic energy generally is not, and the difference is what goes into deformation, heat and sound. That is what a crumple zone is designed to absorb.

The same square explains why speed limits near schools are set where they are. The energy a pedestrian has to absorb rises with the square of the impact speed, and survival rates fall correspondingly steeply between 20 and 40 mph.

How it works

Choose energy, mass or velocity as the unknown.
Enter the other two in kilograms and metres per second.
See the result in joules, plus calories and watt-hours for a sense of scale.

Frequently asked questions

What is the kinetic energy formula?: KE = ½mv², where m is mass in kilograms and v is velocity in metres per second. The result is in joules.
Why does doubling speed quadruple energy?: Because velocity is squared in the formula. Twice the speed is four times the energy, which is why stopping distances and crash severity rise so much faster than speed does.
What is the difference between kinetic energy and momentum?: Momentum is mv and scales linearly; kinetic energy is ½mv² and scales with the square. Momentum is conserved in a collision, kinetic energy usually is not — the difference becomes deformation, heat and sound.
How much energy does a car have at motorway speed?: A 1,500 kg car at 70 mph, about 31 m/s, carries roughly 720 kilojoules — comparable to the energy of a stick of dynamite. All of it has to go somewhere in a crash.
Why do speed limits matter so much near schools?: Because the energy a pedestrian absorbs scales with the square of the impact speed. The difference between 20 and 30 mph is more than double the energy, and survival rates reflect that.

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