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