The formula
Ec = ½ · m · v²
| Symbol | Quantity | Unit |
|---|---|---|
| Ec | Kinetic energy | J |
| m | Mass | kg |
| v | Speed | m/s |
What it means
Kinetic energy is half the mass times the velocity squared. Because the velocity is squared, doubling the speed quadruples the energy, and that is not a detail: it is why a small increase in speed makes such a large difference to a crash.
How to work it out by hand
- Square the velocity
- Multiply by the mass
- Halve the result: the answer is in joules
What is worth knowing
The squared term is the whole public-safety argument. Going from 50 to 70 km/h is a 40 % increase in speed and a 96 % increase in energy — nearly double the damage to dissipate in a collision. It is also why braking distance grows so sharply: the brakes must remove all that energy, and they do it at a roughly constant rate. Doubling the speed roughly quadruples the stopping distance, which is far more than most drivers expect.