Define what is meant by gravitational potential.
Earth E and Moon M may each be modelled as isolated point masses located at their centres. The Earth has mass $5.98 \times 10^{24}\,\text{kg}$ and the Moon has mass $7.35 \times 10^{22}\,\text{kg}$. The separation between the Earth and the Moon is $3.84 \times 10^{8}\,\text{m}$, as shown in Fig. 2.1. $P$ is a point on the line joining the centres of E and M at which the resultant gravitational field strength is zero. Point $P$ is a distance $x$ from the centre of the Earth.
Explain why the gravitational field strength can be zero even when two large masses are nearby.
Show that $x$ has a value of about $3.5 \times 10^{8}\,\text{m}$.
Calculate the gravitational potential, $\phi$, at point $P$.
Calculate the gravitational potential, $\phi$, at point $P$.