Kinetic EnergyFree online science calculator — instant results, no sign-up
Calculate kinetic energy from mass and velocity (KE = ½mv²).
About the Kinetic Energy
The Kinetic Energy calculator finds the energy of motion from an object's mass in kilograms and velocity in meters per second using KE = ½ × m × v². With the default mass of 80 kg and velocity of 10 m/s, it returns 4,000 J, or 4 kJ.
- Mass (kg)
- The object's mass in kilograms (kg), with a default value of 80 kg.
- Velocity (m/s)
- The object's velocity magnitude, or speed, in meters per second (m/s), with a default value of 10 m/s.
Formula and method
KE = ½ × m × v²
- KEKinetic energy, measured in joules (J).
- mThe object's mass, measured in kilograms (kg).
- vThe object's speed relative to the chosen reference frame, measured in meters per second (m/s).
Square the velocity, multiply by the mass, and multiply by one-half to obtain kinetic energy in joules. For the default inputs, KE = ½ × 80 × 10² = 4,000 J. Divide the joule result by 1,000 to express it in kilojoules: 4,000 ÷ 1,000 = 4 kJ.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Mass80 kg
- Velocity10 m/s
Results
- Kinetic energy4,000 J
- In kilojoules4 kJ
- FormulaKE = ½ × m × v²
How to use the Kinetic Energy
- 1Enter the object's mass in Mass (kg); use 80 for the default example.
- 2Enter its speed in Velocity (m/s); use 10 for the default example.
- 3Check that mass is nonnegative and that both inputs use the stated units.
- 4Run the calculation to apply KE = ½ × m × v².
- 5Read the results in joules and kilojoules; the default inputs give 4,000 J and 4 kJ.
Reading your result
The Kinetic energy row reports the calculated energy of motion in joules: 4,000 J for the default inputs. The In kilojoules row reports the same energy on a different scale: 4 kJ, since 1 kJ = 1,000 J. The Formula row shows the relationship used, KE = ½ × m × v²; velocity is squared, so its effect is not linear.
Limitations
This calculator uses classical mechanics and is appropriate for speeds much smaller than the speed of light; relativistic speeds require a different formula. It calculates translational kinetic energy and does not include rotational, potential, or internal energy. Speed must be measured relative to a specified reference frame, because kinetic energy depends on that frame. Negative mass is not physically valid here. Input precision limits result precision, and the result alone does not determine stopping distance or impact force.
Common questions
Why do 80 kg and 10 m/s produce 4,000 J?+
Squaring 10 m/s gives 100 m²/s². Multiplying by 80 kg and then by one-half gives 4,000 kg·m²/s², equivalent to 4,000 J.
Why does velocity affect kinetic energy more strongly than mass?+
Mass enters the formula linearly, while velocity is squared. Holding speed constant, doubling mass doubles kinetic energy; holding mass constant, doubling speed quadruples kinetic energy.
Does reversing the direction of motion change the result?+
No, provided the speed stays the same in the same reference frame. Kinetic energy is a scalar, and squaring a signed velocity gives the same result for either direction.
Can I use the kinetic energy result to calculate impact force?+
Not from kinetic energy alone. Estimating average stopping force from energy also requires a stopping distance and assumptions about how that energy is transferred; peak impact force requires more detail.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.