Lift something and you store energy in it. That stored energy — gravitational potential energy — is exactly the work you did against gravity: the object's weight (mass × g) multiplied by the height you raised it. Let it go and the store empties: the PE converts into kinetic energy as it falls, so that the speed it lands at depends only on the drop height, never the mass. PE = mgh is one of the simplest and most useful equations in physics, behind everything from hydro dams to a swinging pendulum.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: gravitational potential energy and energy conservation.
The potential-energy equations
With mass in kilograms, g in metres per second squared and height in metres, PE comes out in joules. The energy-conservation link is the elegant part: set the kinetic energy at the bottom equal to the potential energy at the top and the mass cancels, leaving v = √(2gh) — the same impact speed a free-fall calculation gives. Only the change in height matters, so you measure PE from whatever zero level is convenient.
Worked example — lifting and dropping
Scenario: A 10 kg mass is raised 5 m, then released (g = 9.81 m/s²).
Lifting the mass stored 490.5 J. When dropped, all of that becomes kinetic energy and it hits the ground at 9.9 m/s — and a 20 kg mass from the same height would land at the same speed, just with twice the energy (981 J). On the Moon (g = 1.62) the stored energy and impact speed are far smaller, which is the whole reason things feel "lighter" there: less weight means less PE for the same height.
Frequently Asked Questions
PE = m × g × h. A 10 kg mass at 5 m has 10 × 9.81 × 5 = 490.5 J. It's the energy stored by lifting.
Joules (J); 1 kJ = 1000 J. kg × m/s² × m gives joules directly.
They convert: falling turns PE into KE. ½mv² = mgh, so impact speed v = √(2gh) — mass cancels.
Yes — PE is relative to a chosen zero (floor, table). Only the height change matters physically.
Equals the PE gained: mgh. A 20 kg box up 2 m needs 392.4 J, regardless of how fast you lift it.