MotionLab

Kinetic Energy Calculator

KE = ½ · m · v², in joules.

Mass (kg)

Velocity (m/s)

Kinetic energy (J)

875

KE = ½ · m · v²

What you entered

Mass (kg): 70Velocity (m/s): 5

1
Square the velocity
5²= 25
2
Multiply by ½ × mass
0.5 × 70 × 25= 875

Result

Kinetic energy (J): 875

A 70kg mass moving at 5 m/s carries 875 joules of kinetic energy.

Kinetic energy of moving objects

Kinetic energy is half the mass times the velocity squared. Because velocity is squared, speed matters far more than mass.

Mass (kg)	Velocity (m/s)	Kinetic energy (J)	Object
1	1	0.50	Unit case
0.145	40	116.00	Baseball at 90 mph
70	5	875.00	Sprinting person
1000	10	50000.00	Car at 36 km/h
1000	20	200000.00	Car at 72 km/h
1000	30	450000.00	Car at 108 km/h

The last three rows are the road-safety argument in three lines: doubling the speed from 10 to 20 m/s quadruples the energy, and tripling it to 30 multiplies it by nine. That energy has to go somewhere in a crash, which is why stopping distances and impact severity rise so steeply with speed while the mass stays the same. Compare the baseball and the sprinter - the person has 500 times the mass but only about 7.5 times the energy, because the ball is moving eight times faster.

Why velocity is squared

Kinetic energy grows with the square of velocity, not linearly — doubling a car's speed quadruples its kinetic energy, which is exactly why higher-speed collisions are so disproportionately more dangerous.

Where it's applied

Vehicle safety engineering, sports science (impact force in collisions), and basic physics problems involving falling or moving objects all use this exact formula.

Frequently asked questions

A 1,500 kg car travelling at 30 m/s crashes. How much kinetic energy is released?

KE = ½ × 1500 × 30² = 675,000 joules = 675 kJ. At 60 m/s (double the speed), KE = 2,700 kJ — four times as much. This is why speed limits save lives: doubling speed quadruples crash energy.

How is kinetic energy different from potential energy?

Kinetic energy is energy of motion (depends on speed). Potential energy is stored energy from position (depends on height or compression). A ball at the top of a hill has max potential energy; at the bottom, max kinetic. Energy converts between the two. See the potential energy calculator.

Why does kinetic energy depend on velocity squared?

Because work = force × distance, and a faster object travels more distance during the same deceleration. Doubling speed means the brakes must absorb 4× the energy over 4× the stopping distance. This v² relationship is fundamental to vehicle safety, ballistics, and wind energy.