Calculators
Kinetic Energy Calculator
Solve kinetic energy, mass, or speed with unit conversion.
Kinetic Energy Calculator tool
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About This Tool
Kinetic energy is the energy an object has because of its motion. For ordinary non-relativistic translation, it depends on mass and the square of speed, so doubling speed produces four times the kinetic energy when mass stays the same. This calculator solves KE = ½mv² in all three directions: find kinetic energy from mass and speed, find mass from kinetic energy and speed, or find speed from kinetic energy and mass. Unit conversions are handled before the formula is applied, and the calculation stays in your browser.
How To Use It
- Choose whether to solve for kinetic energy, mass, or speed.
- Enter the two known values and select their units. Zero is valid when directly calculating kinetic energy, but inverse solves need a non-zero divisor.
- Choose the desired result unit and review the equation shown with the result.
- Interpret the answer as classical translational kinetic energy in the chosen reference frame; other forms of energy are not included.
Examples
2 kg moving at 3 m/s
KE = ½ × 2 × 3² = 9 J.
1 kg moving at 36 km/h
36 km/h equals 10 m/s, so KE = ½ × 1 × 10² = 50 J.
Find speed
An object with mass 2 kg and kinetic energy 100 J has speed √(2 × 100 ÷ 2) = 10 m/s.
Why speed matters strongly
For the same mass, increasing speed from 10 m/s to 20 m/s multiplies kinetic energy by four because speed is squared.
Useful Notes
Kinetic energy formula
The classical translational formula is KE = ½mv², where KE is energy, m is mass, and v is speed. In SI units, kilograms and metres per second produce joules.
Solving for mass or speed
Rearranging the same equation gives m = 2KE/v² and v = √(2KE/m). A zero speed cannot be used to infer mass from a nonzero energy, and zero mass cannot be used to infer speed.
Unit conversions
Mass inputs support kilograms, grams, and pounds. Speed supports metres per second, kilometres per hour, miles per hour, and feet per second. Energy supports joules, kilojoules, thermochemical calories, and watt-hours.
Reference frame matters
Kinetic energy depends on the measured speed, and speed depends on the observer's reference frame. Two observers moving relative to one another can therefore assign different translational kinetic energies to the same object.
Classical model limitation
KE = ½mv² is the standard classical expression for everyday speeds. At speeds that are a substantial fraction of the speed of light, relativistic kinetic energy is required instead.
What the result does not include
The result is translational kinetic energy only. It does not automatically include rotational kinetic energy, gravitational or elastic potential energy, deformation, friction, drag, heat, or losses in a real process.
FAQ
What is the SI unit of kinetic energy?
The SI unit is the joule (J), equivalent to kg·m²/s².
Can kinetic energy be zero?
Yes. In the classical formula, an object with zero speed has zero translational kinetic energy in that reference frame. A zero-mass mathematical input also produces zero in the direct calculation, although ordinary physical objects have positive mass.
Can kinetic energy be negative?
Not with the classical translational expression KE = ½mv² for non-negative mass. This calculator rejects negative mass, speed, and energy inputs.
Does direction affect kinetic energy?
No. Translational kinetic energy depends on speed, the magnitude of velocity, so reversing direction without changing speed leaves KE unchanged.
Is this the same as rotational kinetic energy?
No. Rotational kinetic energy uses ½Iω², where I is moment of inertia and ω is angular velocity. This tool calculates translational kinetic energy from mass and linear speed.