Case 1
- Mass
- 1000kg
- Speed
- 20m/s
200,000.000J
Open with these valuesKinetic Energy Calculator
200,000.000J
Result: 200,000.000 JHalf the mass times the speed squared. Because the speed is squared, doubling it quadruples the energy: a 1000 kg car carries 200 kJ at 20 m/s and 800 kJ at 40 m/s. Enter kilograms and metres per second and the answer comes back in joules.
Worked examples
Case 2
- Mass
- 0.145kg
- Speed
- 40m/s
116.000J
Open with these valuesCase 3
- Mass
- 80kg
- Speed
- 10m/s
4,000.000J
Open with these valuesHow it's calculated
KE = ½ × m × v²
- StepEnter the mass in kilograms.
- StepEnter the speed in metres per second — divide km/h by 3.6.
- ResultRead the kinetic energy in joules; 1000 J is one kilojoule.
What this number means
Twice the speed, four times the energy
The speed is squared, which makes it by far the stronger of the two inputs: the same 1000 kg car carries 200 kJ at 20 m/s and 800 kJ at 40 m/s. Doubling the mass instead would only double the energy.
A baseball out-punches a thrown brick
The brick has almost fourteen times the mass of the ball, 2 kg against 0.145 kg. But it leaves the hand at 3 m/s while the ball leaves it at 40 m/s, and squaring that gap settles it: 116 J for the ball, 9 J for the brick.
Why stopping distances grow so steeply
Before a car stands still, every joule of this has to go somewhere — into heat, sound or deformation. Because the total grows with v², a modest gain in speed is a large gain in what brakes or crash structures have to absorb.
Convert km/h before you type
Joules only come out if the mass is in kilograms and the speed in metres per second, so divide km/h by 3.6 first. A car at 72 km/h is 20 m/s and carries 200 kJ; entering 72 would report nearly thirteen times that.
Commonly misread
Twice as fast means twice the energy.
It means four times as much, because the speed is squared: 200 kJ at 20 m/s becomes 800 kJ at 40 m/s, and three times the speed means nine times the energy.
Kinetic energy and momentum are two names for the same thing.
Momentum is m × v and grows in step with the speed, while kinetic energy is ½mv² and grows with its square. One is a vector in kg·m/s, the other a scalar in joules.
A car reversing at 20 m/s must have negative kinetic energy.
Squaring the speed removes the sign, so it is the same 200 kJ whichever way the car moves. Only momentum carries a direction; this box takes the speed, not the velocity.
Reference table
| Mass, speed | Example | Energy (J) |
|---|---|---|
| 1, 1 | One kilogram, walking pace | 0.5 |
| 2, 3 | A brick, thrown | 9 |
| 0.145, 40 | Pitched baseball | 116 |
| 80, 10 | Sprinter at full speed | 4000 |
| 1000, 20 | Small car at 72 km/h | 200000 |
Questions
How do I calculate kinetic energy?
Multiply half the mass by the velocity squared: KE = ½ × m × v². Use kilograms for mass and metres per second for velocity to get the answer in joules. For example, a 1000 kg car at 20 m/s has ½ × 1000 × 20² = 200,000 J (200 kJ).
What is kinetic energy?
Kinetic energy is the energy an object possesses because it is moving. Any object with mass that is in motion carries kinetic energy, and the faster or heavier it is, the more it has. It is measured in joules (J), the same unit used for every other form of energy.
Why does doubling the speed quadruple the energy?
Because velocity is squared in the formula. Energy scales with v², so doubling the speed multiplies the kinetic energy by 2² = 4, and tripling it multiplies the energy by nine. This is why stopping distances grow so steeply with speed and why high-speed impacts are so much more destructive.
What is the difference between kinetic energy and momentum?
Momentum is mass times velocity (p = mv) and grows in proportion to speed, while kinetic energy uses velocity squared (½mv²) and grows much faster. Momentum is a vector with direction and is conserved in collisions; kinetic energy is a scalar measured in joules and can convert into heat, sound, or deformation.
What units should I use for kinetic energy?
Use SI units: kilograms for mass and metres per second for velocity, which gives kinetic energy in joules. If your speed is in km/h, divide by 3.6 to convert to m/s first. One joule equals one kg·m²/s², and 1000 joules make one kilojoule (kJ).
Sources and last check
Information, not professional advice.