Gravitational Potential Energy (SL IB Physics)

• Gravitational potential energy E_p is the energy stored in a mass due to its position in a gravitational field
  • If a mass is lifted up, it will gain E_p (converted from other forms of energy)
  • If a mass falls, it will lose E_p (and be converted to other forms of 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 (9.81 N kg^–1)
  • Δh = change in height (m)

Gravitational potential energy (GPE): The energy an object has when lifted up

• The potential energy on the Earth’s surface at ground level is taken to be equal to 0
• 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

GPE vs Height

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

Graphs showing the linear relationship between GPE and height

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