Kinetic Energy Calculator
Calculate the kinetic energy (energy of motion) of an object based on mass and velocity.
How to use the kinetic energy calculator
- Enter the mass of the object in kilograms.
- Enter the velocity in meters per second.
- The result updates automatically as you type.
The formula for kinetic energy
Worked example: a 1000 kg car at 20 m/s (72 km/h) has a kinetic energy of ½ × 1000 × 20² = 200,000 J, or 200 kJ. Double the speed to 40 m/s and the energy becomes ½ × 1000 × 40² = 800,000 J — four times as much, since velocity enters the formula squared.
Kinetic energy (E), also called energy of motion, is the energy an object has because it is moving. It's calculated from half the mass (m) multiplied by the velocity (v) squared, and is measured in joules (J).
Notice that velocity is squared in the formula — that means the energy quadruples if the speed doubles, not just doubles. This is a key reason a car's braking distance increases far more than proportionally with speed: drive twice as fast, and you need (in theory) four times as much energy to stop.
Frequently asked questions
Why is kinetic energy so sensitive to speed changes?
Because velocity enters the formula squared (v²). Double the speed, and the kinetic energy quadruples. This squared relationship means even small speed increases can produce large changes in the amount of energy.
What is kinetic energy measured in?
Kinetic energy is measured in joules (J), the same unit as all other energy in physics. For large values, such as cars in motion, it's often practical to give the result in kilojoules (kJ).
How does this relate to a car's braking distance?
The brakes must convert the car's kinetic energy into heat to stop it. Since the energy increases with the square of the speed, braking distance also increases much faster than speed — this is a major reason high speed is so dangerous in traffic.