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Kinetic energy is the energy an object has because it's moving. It grows with mass, but it grows with the *square* of speed — so doubling the speed quadruples the energy. That's why a small increase in velocity has such an outsized effect in collisions.
Choose what you want to find, enter the values you know, and get the energy in joules.
Kinetic Energy Calculator: step-by-step worked example
- Solve for
- Kinetic energy (from mass & speed)
- Mass (kg)
- 1,500
- Speed (m/s)
- 25
- 1
Square the speed
v²
25 × 25 = 625 m²/s²
- 2
Kinetic energy
KE = ½ × m × v²
0.5 × 1,500 × 625 = 468,750 J
- 3
In kilojoules
kJ = J ÷ 1,000
468,750 ÷ 1,000 = 468.75 kJ
- 1500 kg:0 kJ → 1,875 kJ
Good to know: Energy grows with the square of speed: a car at 90 km/h (56 mph) carries four times the energy of one at 45 km/h — braking distance grows roughly the same way.
Kinetic Energy Calculator — how it works
The kinetic energy relation
| Solve for | Formula |
|---|---|
| Kinetic energy KE (J) | ½ × mass × speed² |
| Mass m (kg) | 2 × KE ÷ speed² |
| Speed v (m/s) | √(2 × KE ÷ mass) |
Mass is in kilograms and speed in metres per second, giving energy in joules (J).
Speed dominates
Because the speed is squared, it matters far more than the mass. Doubling the mass doubles the energy, but doubling the speed multiplies it by four; tripling the speed multiplies it by nine. This is the physics behind why braking distance rises sharply with speed and why high-speed impacts are so much more severe.
Kinetic vs potential energy
Kinetic energy is the energy of motion; potential energy is stored energy (gravitational, elastic). As an object falls, potential converts to kinetic — a ball at the top of a drop has all potential energy and none kinetic; just before impact it's the reverse. Total mechanical energy is conserved when friction is negligible.
Where it helps
Impact and collision analysis, projectile physics, roller-coaster and vehicle problems, and homework. To first find the speed from distance and time, use a speed calculator; for the momentum of the same object, a momentum calculator.
Worked example
A 1,000 kg car travelling at 20 m/s (72 km/h) has kinetic energy KE = ½ × 1,000 × 20² = ½ × 1,000 × 400 = 200,000 J (200 kJ). Speed up to 40 m/s and the energy is ½ × 1,000 × 1,600 = 800,000 J — four times as much for double the speed, which is exactly why stopping distances balloon at higher speeds.
Frequently asked questions
What is kinetic energy?+
Kinetic energy is the energy an object has due to its motion, given by KE = ½ · m · v². A stationary object has zero kinetic energy.
Why is speed squared in the formula?+
Because energy depends on the square of velocity, speed affects kinetic energy far more than mass. Doubling the speed quadruples the energy; tripling it multiplies the energy ninefold.
What units does kinetic energy use?+
The joule (J), when mass is in kilograms and speed in metres per second. One joule is one kg·m²/s². Convert km/h to m/s (÷ 3.6) before entering a speed.
How do I find the speed from kinetic energy?+
Rearrange to v = √(2 × KE ÷ m). Choose "Speed" mode and enter the energy and mass; the tool takes the square root for you.
What is the difference between kinetic and potential energy?+
Kinetic energy is the energy of motion; potential energy is stored (for example due to height). As something falls, potential energy converts into kinetic energy.
About this page
- Publisher:
- Kalkoro — Teknolojig Bilişim Teknolojileri A.Ş., İstanbul
- Written by:
- Ahmet Tur — Editor (Math, date & time, unit conversion, physics & chemistry, everyday tools)
- Reviewed by:
- Kübra Yıldız — Editor
Parameters come from official sources; the last update date is shown at the bottom of the page.
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