By Zencalcy Editorial TeamLast reviewed About us
Kinetic energy is the energy an object carries because it is moving. It grows with the square of speed, so a car at 100 km/h has four times the kinetic energy it has at 50 km/h — which is why stopping distances grow so quickly with speed.
Energy of motion from mass and speed.
E_k = ½ m v²
E_k is kinetic energy in joules, m is mass in kilograms and v is speed in metres per second. The formula applies at everyday speeds; near the speed of light the relativistic form is needed.
| Symbol | Meaning |
|---|---|
| E_k | Kinetic energy, in joules. |
| m | Mass, in kilograms. |
| v | Speed, in metres per second. |
E_k = 0.5 × 2 × 3² = 9 J. Doubling the speed to 6 m/s raises the energy to 36 J — a factor of four for a factor of two in speed.
Continue with the Mechanical Energy Calculator, Potential Energy Calculator, or the Power Calculator — or browse more work, energy and power tools and all physics calculators.
The work needed to accelerate an object is force times distance. A constant force applied for a fixed time produces speed proportional to time and distance proportional to time squared, so the work scales with v².
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026