Kinetic Energy Calculator
Calculate kinetic energy (KE = ½mv²) in joules, kilojoules, kilocalories, and foot-pounds.
Kinetic Energy Examples
| Object | Mass | Speed | KE |
|---|---|---|---|
| Walking person | 70 kg | 1.4 m/s | 69 J |
| Pitched baseball | 145 g | 40 m/s | 116 J |
| Car at 60 km/h | 1,400 kg | 16.7 m/s | 194 kJ |
| Car at 100 km/h | 1,400 kg | 27.8 m/s | 540 kJ |
| Bullet (9mm) | 8 g | 370 m/s | 548 J |
Frequently Asked Questions
What is kinetic energy?
Kinetic energy is the energy an object possesses due to its motion. Any moving object has kinetic energy. The formula is KE = ½mv², where m is mass in kilograms and v is velocity in metres per second. The result is in joules (J). Kinetic energy is always positive (or zero if at rest) and increases with the square of velocity — doubling speed quadruples kinetic energy.
What is a joule?
A joule (J) is the SI unit of energy. One joule equals the kinetic energy of a 2 kg mass moving at 1 m/s (KE = ½ × 2 × 1² = 1 J). It is also the energy needed to lift a 100 g apple 1 metre off the ground. Larger quantities of energy are commonly expressed in kilojoules (kJ = 1,000 J) or megajoules (MJ = 1,000,000 J).
Why does speed have a greater effect than mass on kinetic energy?
Because kinetic energy is proportional to velocity squared (v²) but only linearly proportional to mass (m). Doubling the mass doubles kinetic energy. Doubling the speed quadruples kinetic energy. This is why high-speed collisions are so much more dangerous than slow ones — a car at 60 mph has four times the kinetic energy of the same car at 30 mph.
What is kinetic energy in everyday terms?
A 70 kg person walking at 1.4 m/s (3 mph) has about 69 J of kinetic energy. A 1,400 kg car at 60 km/h (16.7 m/s) has about 194,000 J (194 kJ). A pitched baseball (0.145 kg at 40 m/s) has about 116 J. These numbers explain why car crashes are so destructive — the kinetic energy must be absorbed somewhere.
What happens to kinetic energy in a collision?
In a perfectly elastic collision, total kinetic energy is conserved — both objects bounce off and the total KE is unchanged. In an inelastic collision (like a car crash), kinetic energy is converted to heat, sound, and deformation. In a perfectly inelastic collision, the objects stick together and maximum kinetic energy is lost (though momentum is always conserved).