Practise defining gravitational field strength, interpreting radial field diagrams, applying point or spherical-mass assumptions and describing variation with units.
Define gravitational field.
A spherical planet can be considered as a point mass at its centre.
On Fig. 1.1, draw gravitational field lines outside the planet to represent the gravitational field due to the planet.
Fig. 1.1
State what is indicated by the direction of the gravitational field line at a point in a gravitational field.
A large isolated uniform sphere has mass M and radius R.
Point P lies on a straight line passing through the centre of the sphere, at a variable displacement x from the centre, as shown in Fig. 1.1.
Fig. 1.1
Fig. 1.2 shows the variation with x of the gravitational field g at point P due to the sphere for the values of x for which P is inside the sphere.
Fig. 1.2
The magnitude of the gravitational field at the surface of the sphere is Y.
Explain why, at the surface of the sphere, g always has the opposite sign to x.
Define gravitational field.