Science at key stage 3 (Year 9)
Unit 9J: Gravity and space
Section 6: a. What keeps the planets and satellites in orbit?
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Objectives |
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- that the Sun is massive and exerts a very large gravitational force, which keeps planets in orbit
- to relate the model of circular motion to data on the orbits of planets and satellites
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Activities |
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Outcomes |
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Children: |
- Show pupils a video on the formation of the solar system. Ask them to extract information about the effects of gravity on the resultant shapes and motions of the planets and other bodies. Discuss the main points with pupils.
- Help pupils to make the link between circular motion and inward force by swinging a rubber bung on a string in a circular motion. Point out the tension in the string, which suggests an outward pull by the bung. Help them to realise that the bung's circular motion can only be maintained by an inward force, which is exerted by the string. Ask pupils what would happen if the string were cut. This is a model of the gravitational pull exerted on the planets by the Sun.
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- extract relevant information from a video
- explain that it is the Sun's gravitational force that keeps planets in orbit
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Points to note |
- Pupils will find the link between the Sun's gravity and planetary motion difficult to accept. Many pupils think that something moving in a circle has an inherent circular motion and would continue to move in a circle of its own accord.
Safety
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care is needed with fast-moving objects
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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