Gravitational Potential (OCR A Level Physics)

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Gravitational Potential

Near the Earth's Surface

  • The gravitational potential energy (G.P.E) is the energy an object has when lifted off the ground given by the familiar equation:

G.P.E = mgΔh

  • When using this equation, the G.P.E on the surface of the Earth is taken to be zero
    • This means work is done to lift the object

  • This equation can only be used for objects that are near the Earth's surface
    • This is because, near Earth's surface, the gravitational field is approximated to be uniform
    • Far away from the Earth's surface, the gravitational field is radial because the Earth is a sphere

In a Radial Field

  • In a radial field, G.P.E is defined as the energy an object possesses due to its position in a gravitational field
  • The gravitational potential at a point is the gravitational potential energy per unit of mass for an object at that point
  • Gravity is always attractive, so work must be done on a mass to move it away to a point infinitely far away from every other mass
    • 'Infinity' is the point at which the gravitational potential is zero
    • Therefore, since the potential energy of all masses increases as work is done on them to move them infinitely far away, the value of the potential is always negative

  • Gravitational potential is formally defined as:

The work done per unit of mass in bringing a mass from infinity to a defined point

Gravitational Potential, downloadable AS & A Level Physics revision notes

Gravitational potential decreases as the satellite moves closer to the Earth. It increases if it moves further away, towards infinity, where gravitational potential is zero

Exam Tip

A common exam question requires you to explain the 'negative sign' for values of gravitational potential. Remember the two key facts: 

  • Gravitational fields are always attractive
  • It requires work to move a mass to infinity, where potential is defined as zero

Since the potential energy of a mass therefore increases as it moves toward infinity (where V = 0), the value of the potential everywhere else must be negative

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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