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How to use
Classical kinetic energy equals one half mass times speed squared. Solve for any variable while the calculator converts inputs through SI units internally.
- Choose energy, mass or speed as the unknown.
- Enter the two known values and their units.
- Calculate the result and its SI value.
How it is calculated
Example
Example: a 1500 kg car travels at 72 km/h. First convert speed: 72÷3.6=20 m/s. Then KE=½×1500×20²=300000 J=300 kJ. Kilograms and metres per second give energy in joules. Entering 72 as m/s instead gives a different result because it represents a higher speed.
Important notes
This is the classical formula, not a relativistic one; speeds near the speed of light require relativistic mechanics.
Worked examples and interpreting results
A body of mass 2 kg moving at 3 m/s has kinetic energy 9 J. Doubling its speed to 6 m/s at the same mass raises energy to 36 J because the formula squares speed.
| Case | Calculation | Result |
|---|---|---|
| Energy at 3 m/s | 0.5 × 2 × 3² | 9 J |
| Energy at 6 m/s | 0.5 × 2 × 6² | 36 J |
How to check the result
Use kilograms and meters per second, or select matching units where the form supports them. Energy does not encode the direction of velocity. This is a classical-mechanics formula and needs modification near the speed of light.
Kinetic energy from mass and speed
Translational kinetic energy is half the mass multiplied by the square of speed. Kilograms and metres per second give an answer in joules.
- 2 kg at 3 m/s: 0.5 × 2 × 3² = 9 J
- 1000 kg at 20 m/s: 0.5 × 1000 × 20² = 200000 J
- Energy when speed doubles: (2v)² / v² = 4
Important note
Doubling speed at the same mass quadruples kinetic energy rather than merely doubling it.
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Frequently asked questions
Does the result include the wheels’ rotational energy?
No. The formula ½mv² gives translational kinetic energy at the specified speed. If parts also rotate, their rotational energy is calculated separately using moment of inertia and angular speed.
Can kinetic energy be negative?
Not in this classical formula for positive mass; the calculator uses non-negative speed magnitude.
Which has more influence: mass or speed?
Kinetic energy scales linearly with mass but with the square of speed. Doubling mass doubles the energy, while doubling speed makes it four times larger in the classical model.