Work, Power & Energy Resources

Definition

• Gravitational potential energy (GPE) is the energy an object holds because of its position in a gravitational field, specifically its height above some chosen reference level (usually the ground or floor)
• Lifting an object pushes energy into its gravitational store; letting an object fall pulls energy out

The GPE equation

GPE = m × g × h

• where:
  • GPE = energy in the gravitational potential store (J)
  • m = mass of the object (kg)
  • g is the gravitational field strength of the planet (N/kg). On Earth's surface, g ≈ 10 N/kg
  • h = height above the chosen reference level (m)
• g is given on the exam equation sheet; the Moon's g is about 1.6 N/kg, Jupiter's surface (where there is one) feels about 25 N/kg

Why GPE is linear in h

• For a fixed mass on a given planet, both m and g are constants, so the GPE rises linearly with the height h
• Doubling the height doubles the GPE; halving the height halves the GPE
• A graph of GPE against height is a straight line passing through the origin