Satellites and moons
4 marks · NormalThe planet Neptune is much farther from the Sun than Earth.
State how the gravitational force between Neptune and the Sun compares with that between the Earth and the Sun.
Explain how this difference in gravitational force affects Neptune’s orbit compared to Earth’s.
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(a) The gravitational force between Neptune and the Sun is much weaker than between Earth and the Sun.
(b) Weaker gravity means Neptune’s orbit is less curved and takes much longer to complete; it moves more slowly in its orbit than Earth does. · must show weaker gravitational pull, less curved/less sharp orbit, longer time to orbit
Must show: weaker force for Neptune, less curved path, longer orbital period
Common mistakes: Saying force is the same; Confusing which orbit is longer
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Marking points
B1 (a) · 1 mark · Correctly compares the gravitational forces (Neptune–Sun < Earth–Sun).
B2 (b) · 1 mark · States that weaker gravity means less curved orbit for Neptune.
B3 (b) · 1 mark · States that Neptune moves more slowly in its orbit.
B4 (b) · 1 mark · States orbit takes longer (longer period) than for Earth.
Worked solution
a) The gravitational force between Neptune and the Sun is weaker than that between Earth and the Sun.
b) Because the gravitational force is weaker, Neptune’s orbit is less curved and has a much longer orbital period than Earth. Neptune moves more slowly and takes a longer time to complete an orbit.