Kinetic Energy Calculator
This kinetic energy calculator applies KE = ½mv² to find the kinetic energy of any moving object. Enter the mass and velocity in your preferred units and get kinetic energy in joules, kilojoules, and kWh — plus momentum as a bonus.
Object properties
Enter the mass and velocity of the moving object.
The kinetic energy formula explained
Kinetic energy is derived from Newton's laws and the work-energy theorem. When a constant force accelerates an object from rest to velocity v over distance d, the work done — and hence the energy transferred — equals:
KE = ½ × m × v²
The factor of ½ comes from the integration of momentum over time. Notice that velocity is squared while mass is not — this means a small increase in speed has a much larger effect on energy than the same proportional increase in mass.
Worked example — a car at motorway speed
A 1400 kg car travelling at 110 km/h must be brought to a stop. First convert velocity: 110 km/h = 110 ÷ 3.6 ≈ 30.56 m/s. Then:
KE = ½ × 1400 × 30.56² = ½ × 1400 × 933.9 ≈ 653,700 J ≈ 654 kJ
That 654 kJ of energy must be absorbed by the brakes as heat during an emergency stop — equivalent to roughly 0.18 kWh, enough to boil about 1.5 litres of water. Use the calculator with 1400 kg and 110 km/h to confirm.
Frequently asked questions
- What is kinetic energy?
- Kinetic energy is the energy an object possesses due to its motion. Any object with mass that is moving has kinetic energy. It is a scalar quantity — it has magnitude but no direction — and it is always zero or positive. When an object comes to rest, its kinetic energy is transferred to other forms such as heat, sound, or potential energy.
- What is the formula for kinetic energy?
- Kinetic energy equals one-half times the mass times the velocity squared: KE = ½ × m × v². Mass is in kilograms, velocity in metres per second, and the result is in joules. Because velocity is squared, doubling the speed quadruples the kinetic energy — this is why high-speed collisions are so much more destructive than low-speed ones.
- What units does kinetic energy use?
- In the SI system, kinetic energy is measured in joules (J), where 1 J = 1 kg·m²/s². For very large energies you might see kilojoules (kJ) or megajoules (MJ). In the imperial system, energy is measured in foot-pounds (ft·lb) or British thermal units (BTU). The calculator outputs in joules by default but also shows the result in kJ and kWh for convenience.
- What is momentum and how is it related to kinetic energy?
- Momentum (p) is the product of mass and velocity: p = m × v. Unlike kinetic energy, momentum is a vector — it has both magnitude and direction, and it is conserved in collisions. The relationship between the two is KE = p² ÷ (2m). This calculator shows both KE and momentum so you can see both quantities at once.
- How does doubling speed affect kinetic energy?
- Because kinetic energy depends on velocity squared, doubling the speed multiplies the kinetic energy by four (2² = 4). Tripling the speed multiplies it by nine (3² = 9). This quadratic relationship is why braking distance increases with the square of speed, and why speed limits and speed-reduction measures have such a large safety impact.
- What is the difference between kinetic energy and potential energy?
- Kinetic energy is energy due to motion (KE = ½mv²). Potential energy is stored energy due to position or configuration — for example, gravitational potential energy PE = mgh (mass × g × height). Together they form mechanical energy. In the absence of friction, mechanical energy is conserved: as an object falls, PE converts to KE at the rate PE lost = KE gained.
- What are real-world examples of kinetic energy?
- A 1500 kg car travelling at 100 km/h (27.78 m/s) has KE = ½ × 1500 × 27.78² ≈ 578 kJ — the energy that must be dissipated as heat in the brakes when it stops. A 0.145 kg baseball pitched at 40 m/s has KE ≈ 116 J. A 70 kg runner at 5 m/s (18 km/h) has KE = ½ × 70 × 25 = 875 J.