Draw a graph of the strength of the gravitational field,g, against the distance r from the centre of mass of an object.

Inverse square law

What is gravitational potential energy of a mass

It is the work that would need to be done to move it against the force of gravity.

What is the equation for the gravitational potential energy of a mass,m?

E_{grav} = -GMm/r

Draw the graph of gravitional potential energy vs r to show how the gravitational potential energy varies for Earth.

- What does the gradient of the graph show?

- What is the potential energy at an infinite distance from Earth?

- The gradient of a tangent to the graph gives the value of the gravitional force at that point. The force is greatest at the Earth's surface.

- Potential energy is zero at an infinite distance from the Eartch.

What is gravitional potential at a point,V?

It is the potential energy per unit mass, V = E_{grav}/m .

In a radial field, what is the equation for gravitiational potential at a point,V?

V = - GM/r

Draw the graph of gravitational potential vs r, for a point mass r distance away.

- The gradient of the graph tells you what?

- When is the gravitational potential zero?

- The graident of a tangent to the graph gives the value of g at that point.

- The gravitiational potential,V, is zero at infinity.

What are equipotentials?

Equipotentials show all the points in a field which has the same potential.

What is the gravitational potential at the Earths surface?

63 MjKg^{-1}

What is the equation that gives the linear velocity of a circular orbit of planets due to the centripetal force of gravitational force?

v = (GM/r)^{1/2}

It comes from equation F = - GMm/r^{2} and F = mv^{2}/r