Kinetic Energy Calculator
½mv², and why doubling speed quadruples the damage.
Work out Kinetic Energy. ½mv², and why doubling speed quadruples the damage. Free, with no account and nothing to download.
Standard gravity by definition. Local values run 9.78 to 9.83.
Kinetic energy (joules)
200,000
200 kJ · 47.801 kcal
KE = ½mv². The square is what matters: doubling the speed to 40 m/s quadruples the energy to 800,000 J. This is why crash severity rises so much faster than speed, and why braking distance does too — the brakes must dissipate all of it as heat.
How the Kinetic Energy Calculator works
KE = ½mv². The square is what matters: doubling the speed quadruples the energy. This is why crash severity rises so much faster than speed, and why braking distance does too — the brakes have to dissipate every joule of it as heat.
Also known as: kinetic energy formula · half mv squared calculator · energy of motion calculator · how to calculate kinetic energy
Why the square matters
KE = ½mv². Energy depends on the square of speed, while momentum depends on speed directly, and almost every surprising fact about collisions follows from that difference.
A 1,000 kg car at 20 m/s carries 200 kJ. The same car at 40 m/s carries 800 kJ — four times as much, from twice the speed.
What it explains
Braking distance rises with the square of speed. Brakes remove energy at a roughly constant rate, so four times the energy needs four times the distance to shed — which is why the gap between 30 and 60 is far more than double.
Crash severity behaves the same way. A collision at twice the speed does not do twice the damage; the structure has four times the energy to absorb.
It also explains why speed limits are set where they are. The energy difference between 30 and 40 km/h is 78%, not 33%, and pedestrian survival rates track that curve closely.
Frequently asked questions
What is the kinetic energy formula?
½mv² — half the mass times the velocity squared. A 1,000 kg car at 20 m/s carries 200 kJ.
Why does doubling speed quadruple energy?
Because velocity is squared. Going from 20 to 40 m/s multiplies the energy by four, which is the arithmetic behind why speed limits matter more than they intuitively seem to.
How does this relate to braking distance?
Directly. Brakes remove energy at a roughly constant rate, so four times the energy takes four times the distance — which is why stopping distance rises with the square of speed.
What is kinetic energy measured in?
Joules. This page also shows kilojoules, kilocalories and watt-hours, since those are more familiar scales for large amounts.
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