Kinetic energy is the energy an object has because it is moving. Because speed is squared, doubling the speed quadruples the energy, which is why braking distances grow so quickly at higher speeds.
How to use it
Enter mass and speed. Choose output units such as J, kJ or Wh for comparison with batteries and food energy.
Road safety perspective
A car at 100 km/h carries about 1.56 times the energy it has at 80 km/h; all of it must be absorbed by brakes or, in a crash, by the vehicle and occupants.
Inputs explained
| Field | What to enter |
|---|---|
| Mass | Units: kg, lb, st, g |
| Speed | Units: m/s, km/h, mph |
What each result means
- Kinetic energy = 0.5 × [Mass] × [Speed]^2
- Momentum = [Mass] × [Speed]
Example values
How the main result changes when Speed changes and everything else stays at the example values above:
| Speed (m/s) | Kinetic energy (J) |
|---|---|
| 12.5 | 117,187.5 |
| 18.75 | 263,671.88 |
| 25 | 468,750 |
| 31.25 | 732,421.88 |
| 37.5 | 1,054,687.5 |
| 50 | 1,875,000 |
Formula
KE = ½ × m × v²p = m × vWorked example
A 1,500 kg car at 25 m/s (90 km/h).
KE = 0.5 × 1,500 × 25² = 468,750 J ≈ 469 kJ. Momentum = 37,500 kg·m/s.
Key terms
- Joule
- SI unit of energy; one newton acting over one metre.
- Momentum
- Mass times velocity.
- Work–energy theorem
- Net work done on an object equals its change in kinetic energy.
Frequently asked questions
Why is speed squared?
Kinetic energy comes from the work needed to accelerate a mass, which grows with the square of speed.
Does this work near the speed of light?
No. At relativistic speeds use the relativistic energy formula.
How do I convert J to kWh?
Divide by 3,600,000.
What formula does the Kinetic Energy Calculator use?
KE = ½ × m × v².
Can I work backwards from the result?
Yes. Type the result you want into Kinetic energy and the calculator finds the matching speed.