State what the direction of the gravitational field line at a point in a gravitational field indicates.
Explain, using gravitational field lines, why the gravitational field close to the Earth’s surface is approximately constant for small changes in height.
A large isolated uniform sphere has mass $M$ and radius $R$. Point $P$ is on a straight line through the centre of the sphere, at a variable displacement $x$ from the centre, as shown in Fig. 1.1.
Determine an expression for $Y$ in terms of $M$ and $R$. Identify any additional symbols that you use.
Explain why, at the surface of the sphere, $g$ always has the opposite sign to $x$.
Complete Fig. 1.2 to show how $g$ varies with $x$ for values of $x$ up to $\pm 3R$, for which point $P$ lies outside the sphere.