Motion in the Universe
4 marks · EasyThe planet Venus and a space probe orbiting Earth both move in nearly circular orbits because of gravity.
Name the force responsible for keeping Venus and the space probe in orbit.
Explain why Venus moves faster in its orbit than Neptune does.
State one difference between the orbit of the space probe and the orbit of a comet around the Sun.
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(a) Gravitational force (gravity)
(b) Venus is much closer to the Sun than Neptune, so the gravitational attraction is stronger, causing Venus to move faster in its orbit. · must show Venus is closer to Sun (so gravity stronger), Greater force causes higher orbital speed
(c) A comet has an elongated/elliptical orbit, whereas the space probe’s orbit is nearly circular. Or, a comet orbits the Sun while the space probe orbits the Earth.
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Marking points
B1 (a) · 1 mark · States 'gravity' or 'gravitational force'.
B2 (b) · 1 mark · Identifies Venus is closer to the Sun (so gravity is stronger).
B3 (b) · 1 mark · Correctly links stronger gravity to higher orbital speed.
B4 (c) · 1 mark · States a correct difference (e.g. orbit shape, what is orbited).
Worked solution
a) The force is gravity or gravitational force.
b) Venus is much closer to the Sun than Neptune. The gravitational pull from the Sun is stronger on Venus, causing it to move faster in its orbit around the Sun.
c) A space probe around Earth travels in a nearly circular orbit, while a comet around the Sun has a highly elongated or elliptical orbit. Also, the probe orbits the Earth but the comet orbits the Sun.