Satellites and moons
3 marks · NormalBelow is a simple diagram showing a planet and its moon.
On the diagram, draw an arrow to show the direction of the gravitational force acting on the moon.
Explain why this force does not pull the moon directly into the planet.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Arrow from the moon directly towards planet centre. · must show arrow direction
(b) The moon is moving at right angles to the force; gravity continually changes its direction and keeps it in orbit instead of pulling it straight in. · must show Moon’s motion is perpendicular to gravity, Explanation that results in orbit
Must show: arrow from moon towards planet, explanation of orbital path
Common mistakes: Arrow in wrong direction; Not stating orbital motion
Show mark scheme and worked solution
Marking points
D1 (a) · 1 mark · Correct arrow drawn from moon, pointing exactly at the planet’s centre.
B1 (b) · 1 mark · Explains moon’s velocity is at right angles to force/gravity.
B2 (b) · 1 mark · States gravity changes direction, keeping moon in orbit, not pulling it in directly.
Worked solution
b) The moon’s direction of motion is at right angles to the force of gravity, so it stays in orbit rather than falling into the planet. Gravity changes its direction, not its speed towards the planet.