Kinetic energy is the energy of motion
Anything moving carries energy. For a mass m travelling at speed v, that energy is one half of m times v squared — measured in joules.
Double the mass and the energy doubles. Double the speed and it quadruples, because v is squared. That single fact explains a lot of the physical world.
Why speed matters more than mass
A car at 60 km/h carries four times the kinetic energy it had at 30 — not twice. It is why stopping distances and crash forces climb so steeply with speed, and why a small fast object can hit harder than a large slow one.
| Object | Energy |
|---|---|
| Walking person (70 kg, 1.4 m/s) | ~69 J |
| Cyclist (90 kg, 8 m/s) | ~2,880 J |
| Car (1200 kg, 14 m/s) | ~118,000 J |
| Rifle bullet (4 g, 900 m/s) | ~1,620 J |
The bullet weighs almost nothing yet rivals the cyclist — all because of that squared speed.
Where the energy goes
Kinetic energy is never destroyed, only converted. Brakes turn it into heat, a crash into bent metal and sound. The calculator shows the energy an object carries before any of that happens.
Frequently asked questions
What is the kinetic energy formula?
KE = ½ m v², where m is mass in kilograms and v is speed in metres per second. The result is in joules. A 1200 kg car at 14 m/s (about 50 km/h) carries roughly 118,000 J.
How does speed affect kinetic energy?
Much more than mass, because speed is squared. Doubling the speed multiplies the energy by four; tripling it multiplies by nine. Doubling the mass only doubles the energy.
What are the units of kinetic energy?
Joules (J) in SI. One joule is one kilogram-metre-squared per second-squared (kg·m²/s²). Everyday numbers run from a few joules for a walking person to hundreds of thousands for a moving car.
What is the difference between kinetic and potential energy?
Kinetic energy is the energy of motion (½mv²); potential energy is stored energy waiting to be released, such as height (mgh) or a stretched spring. One converts into the other, for example as something falls.
Does mass or speed matter more for kinetic energy?
Speed, because the formula squares it. A light, fast object can carry more energy than a heavy, slow one — which is why a small bullet does so much damage.