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Kinetic energy
Beginner
Energy of motion.
K = ½mv²The energy of motion K = ½mv². It is a scalar, never negative, and grows with the square of speed.
A 1000 kg car at 20 m/s: K = 200 kJ; at 40 m/s: 800 kJ.
Doubling the speed quadruples the kinetic energy and the braking distance.
In more detail
Kinetic energy is the energy of motion, KE = ½mv². It depends on the square of speed, so doubling speed quadruples kinetic energy.
Real-world uses
- Braking distance grows with kinetic energy, which is why higher speeds are much more dangerous.
- Wind turbines capture kinetic energy from moving air.
- A moving car has kinetic energy, so doubling its speed quadruples the energy the brakes must remove to stop it.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Is kinetic energy a vector?
No. It is a scalar, so it has no direction.
Why does speed matter more than mass?
Because kinetic energy depends on the square of speed but only linearly on mass.
Why does kinetic energy depend on the square of speed?
The work to speed up an object is force times distance, and both grow with speed, so the total energy scales with v squared.
Related topics in Work, Energy & Power
Work from a force–displacement graph · Work done by a variable force · Work done by a spring · Work–energy theorem · Potential energy · Gravitational potential energy