Gravitational Potential Energy (HL IB Physics)

• Gravitational potential energy is the energy stored in a mass due to its position in a gravitational field
  • If a mass is lifted up, it will gain gravitational potential energy
  • If a mass falls, it will lose gravitational potential energy

• The equation for gravitational potential energy when close to the surface of the Earth is:

• Where:
  • ΔE_p = gravitational potential energy (J)
  • m = mass (kg)
  • g = gravitational field strength (9.8 N kg^–1)
  • Δh = change in height (m)

Gravitational potential energy: The energy an object has when lifted up

• The potential energy on the Earth’s surface at ground level is usually taken to be equal to zero
  • However, any position can be taken as zero if you are calculating the change in gravitational potential energy
• This equation is only relevant for energy changes in a uniform gravitational field (such as near the Earth’s surface)
• A different potential energy is used in the gravitational fields topic, because the field is no longer uniform outside of the Earth's surface

Gravitational Potential Energy vs Height

• The two graphs below show how the gravitational potential energy changes with height for a ball being thrown up in the air and then falling down (ignoring air resistance)

Graphs showing the linear relationship between gravitational potential energy and height

• Since the graphs are straight lines, gravitational potential energy and height are said to have a linear relationship
  • These graphs would be identical for gravitational potential energy against time instead of height