An object raised above the ground gains energy in its gravitational potential energy store. The change in gravitational potential energy is found with the equation: change in gravitational potential energy = mass × gravitational field strength × change in vertical height, or GPE = m × g × h.
The units are joules (J) for energy, kilograms (kg) for mass, metres (m) for height and newton per kilogram (N/kg) for gravitational field strength. On the surface of the Earth we take g = 10 N/kg. It is smaller on the Moon, so the same object gains less energy when lifted the same height there.
Only the vertical height matters. Carrying a box up a ramp or lifting it straight up through the same height gives the same change in gravitational potential energy. The change is directly proportional to the mass, so doubling the mass doubles the energy gained.
Example: a 2 kg book is lifted 1.5 m. Change in GPE = 2 × 10 × 1.5 = 30 J. The equation can be rearranged: if a 3 kg object gains 60 J, then h = 60 ÷ (3 × 10) = 2 m. A 6 kg object lifted through the same 2 m gains 120 J.