AQA · Physics · 8463
GCSE Physics: Orbital motion, natural and artificial satellites
Space physics · AQA GCSE Physics (8463), specification point 4.8.1.3. Cards are generated from the exam board's own specification for "Orbital motion, natural and artificial satellites", and every card links back to the page it came from. Separate science only. Specification © AQA — used with attribution.
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Which force keeps planets and satellites in their circular orbits?
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Gravity.
? provides the force that allows planets and satellites to maintain their circular orbits.
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Gravity
What is a natural satellite? Give an example.
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A naturally occurring body that orbits a planet — e.g. the Moon orbiting Earth.
What is an artificial satellite?
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A human-made object placed in orbit around a planet (e.g. a communications or weather satellite).
What do planets orbit, and what do moons orbit?
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Planets orbit a star (the Sun); moons orbit planets.
In a circular orbit, why does the velocity change while the speed stays constant?
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Gravity acts at right angles to the motion, so it continually changes the direction of travel (hence velocity) without changing the magnitude (speed).
In which direction does gravity act on a satellite in circular orbit?
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Towards the centre of the orbit (the body it orbits), perpendicular to the satellite's velocity.
Why does a satellite in circular orbit accelerate even though its speed is constant?
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Its direction, and therefore its velocity, is constantly changing — a change in velocity is an acceleration (caused by gravity).
For a stable orbit, what must happen to the radius if the satellite's speed changes?
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The radius must change too — a faster speed needs a smaller radius; a slower speed needs a larger radius.
For a stable orbit, if the orbital speed changes then the ? of the orbit must change.
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radius
How does orbital speed depend on the radius of a stable orbit?
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The smaller the orbital radius, the greater the speed needed for a stable orbit (gravity is stronger closer in).
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