Physics Tools
What It Does
Works out kinetic energy, gravitational and elastic potential energy, work, and power — and can solve any of these backwards, for example the speed needed for a given kinetic energy or the angle a force acts at. Everything runs in your browser.
How to Use It
- Pick a mode (kinetic, gravitational PE, elastic PE, work, or power).
- Choose what to solve for, then fill in the remaining values.
- Read the result (in J and kJ where relevant); the equation used is shown below it.
- Click Copy on the result to grab the raw value.
About Energy, Work & Power
Energy is the capacity to do work, and it comes in several mechanical forms. Kinetic energy (½·m·v²) is the energy of motion — it grows with the square of speed, so doubling your speed quadruples your kinetic energy (and your braking distance). Gravitational potential energy (m·g·h) is stored by lifting a mass against gravity, which is why the same height stores far less energy on the Moon than on Earth. Elastic potential energy (½·k·x²) is stored in a stretched or compressed spring and, like kinetic energy, grows with the square of the displacement. Work (F·d·cos θ) is the energy transferred when a force moves something through a distance — and the cos θ factor is the subtle part: only the component of the force along the motion does work, so a force at right angles does none at all. Finally, power (W / t) is the rate of doing work, measured in watts. Because energy is conserved, these quantities convert into one another: the gravitational PE a ball loses falling becomes kinetic energy, and the elastic PE a drawn bow stores becomes the arrow’s kinetic energy on release. Everything here is computed on your device.
Example
Kinetic mode, m = 2 kg, v = 3 m/s → KE = 9 J.
Frequently Asked Questions
What’s the difference between KE and PE?
Kinetic energy is the energy an object has because it is moving (½·m·v²). Potential energy is stored energy due to position or deformation — gravitational PE (m·g·h) from height, or elastic PE (½·k·x²) in a spring. As something falls, PE converts into KE.
Why does work depend on an angle?
Only the part of a force that points along the direction of motion does work, so work is F·d·cos θ. When the force is perpendicular to the motion (θ = 90°), cos θ is zero and no work is done — which is why carrying a bag horizontally does no physical “work” on it.
What’s the difference between energy and power?
Energy (joules) is the total amount transferred; power (watts) is how fast it is transferred — P = W / t. A 100 W bulb uses 100 joules every second. The same job done in half the time needs twice the power.
What units does this use?
Energy and work are in joules (J), with a kilojoule (kJ) restatement shown for convenience; power is in watts (W). Mass is in kilograms, distances and heights in metres, speed in m/s, spring constant in N/m, force in newtons, and the angle in degrees.
Is my data sent to a server?
No. Every calculation runs locally in your browser; nothing you enter is transmitted or stored.