Kinetic Energy Calculator
Compute kinetic energy KE = ½ m v² from mass (kg) and velocity (m/s). Result in joules.
Ec = — J
Kinetic energy: Ec = (1/2)·m·v²
Kinetic energy is what a body holds simply by moving: Ec = (1/2)·m·v², measured in joules, with mass in kg and velocity in m/s. Notice that v shows up squared. Double the speed and the energy goes up four times over, which is the reason a highway-speed crash is so much nastier than one in town. Run the numbers: a 1,500 kg car at 100 km/h (27.8 m/s) packs Ec ≈ 579 kJ ≈ 138 kcal, and a 9 mm bullet (8 g) at 350 m/s carries 490 J. There's also the work-energy theorem, which ties the net work done on a body to its change in kinetic energy: W = ΔEc. Braking distance follows roughly d = v² / (2·μ·g), so it too climbs with the square of the speed.
Applications
You'll find it behind vehicle crash tests (rated in kJ at 50/60 km/h), highway braking distance, forensic ballistics, roller coasters, and free fall, where Ec builds up as potential energy bleeds away. Wind turbines are another case: the kinetic energy of the wind follows (1/2)·ρ·A·v³, which is cubic in wind speed. A small bump in wind speed turns into a huge jump in power.
FAQ
Why does doubling the speed quadruple the energy? The velocity term is squared. So going from 50 to 100 km/h doesn't merely double the crash impact. It makes it four times worse.
Is kinetic energy a vector? No. It's a scalar, always positive or zero, and it has no direction. That sets it apart from momentum, which is a vector, p = m·v.
How does Ec relate to potential energy? When a system is conservative and friction-free, the total mechanical energy stays put: Ec + Ep = constant. Watch a ball drop and you're watching potential energy turn into kinetic energy.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.