An object lifted above the ground stores energy in its gravitational potential energy store. The more mass it has and the higher it is raised, the more energy it stores. The change in gravitational potential energy (GPE) is found with: change in gravitational potential energy (J) = mass (kg) × gravitational field strength (N/kg) × change in vertical height (m), or ΔGPE = m × g × Δh.
At GCSE we use g = 10 N/kg on Earth. Worked examples: a 2 kg book lifted 3 m gains 2 × 10 × 3 = 60 J. A 50 kg climber who rises 4 m gains 50 × 10 × 4 = 2000 J. A 4 kg object raised 5 m gains 4 × 10 × 5 = 200 J.
Because the three quantities are multiplied together, if the mass is doubled the change in gravitational potential energy is doubled, and the same happens if the height raised is doubled. Only the vertical change in height counts, not the distance travelled along a slope. Energy is measured in joules (J), and 1 J is the same as 1 newton-metre (N m).