How this calculator works
Kinetic energy measures translational motion. The classical expression assumes speed is small compared with light speed and excludes rotation. Speed is a magnitude; mass must be positive. A stationary object has zero kinetic energy. Solving for mass needs positive speed.
Formula
E = m v^2/2; m = 2E/v^2; v = sqrt(2E/m). 1 ft lbf = 1.3558179483314004 J.
Worked example
A 2 kg object moving at 3 m/s has 9 J of kinetic energy. At 6 m/s the same mass has 36 J.
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Frequently asked questions
Does direction matter?
No. Speed is squared, so equal speeds in opposite directions have equal kinetic energies.
Does this include rotation?
No. A rolling body also stores rotational energy about its centre.
Why does doubling speed matter so much?
Energy scales with speed squared: doubling speed multiplies energy by four.