How to calculate kinetic energy
A moving object carries kinetic energy. Speed matters strongly: doubling speed makes this energy four times larger when mass is unchanged.
What the formula is saying
Square the speed, multiply by mass, then divide by two: KE = ½mv². The square makes the translational kinetic energy nonnegative.
Read the symbols in plain language
- m
- Masskg
- v
- Speedm/s
Sort out the units first
Use kg and m/s for joules. To convert km/h to m/s divide by 3.6. The example uses 3 m/s, not 3 km/h.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
- m · Mass
- 20 kg
- v · Speed
- 3 m/s
Square the speed
Multiply speed by itself, not by two.
(3)^2 = 9 m²/s²Multiply by half the mass
The combined unit kg·m²/s² is the joule.
0.5 × (20) × (9) = 90 J
Does this worked answer make sense?
Zero speed gives zero translational kinetic energy. In the example, ½ × 20 × 9 = 90 J.
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Use these new values. Work it out first, then check your answer.
- m · Mass
- 50 kg
- v · Speed
- 2 m/s
Find: kinetic energy
A hint, not the answer
Square the speed, multiply by mass, then divide by two: KE = ½mv². The square makes the translational kinetic energy nonnegative.
Use kg and m/s for joules. To convert km/h to m/s divide by 3.6. The example uses 3 m/s, not 3 km/h.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Square the speed
Multiply speed by itself, not by two.
(2)^2 = 4 m²/s²Multiply by half the mass
The combined unit kg·m²/s² is the joule.
0.5 × (50) × (4) = 100 J
Avoid the common trap
½mv is not kinetic energy; it is missing one velocity factor. Energy is not a force and is not measured in newtons.
When this method applies — and when it does not
Translational kinetic energy in a chosen reference frame at nonrelativistic speeds. Rotating bodies may also have rotational kinetic energy.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Lesson updated: · Worked examples checked against the implemented formula; not an independent engineering certification.