- Remind pupils that when an object floats its weight is balanced by the upthrust. Ask them to suggest why we cannot float in air. Demonstrate a number of situations in which there are easily identifiable balanced forces on a stationary object,
eg a tug of war, a paper clip or magnet held up by magnetic attraction or repulsion, a helium balloon floating at a fixed height, and ask pupils to identify the forces, and the directions in which they are acting. Extend to other contexts,
eg a book resting on a table, an object suspended from a string. Test pupils' understanding by showing them diagrams in which forces of given magnitude are represented by arrows and ask them questions,
eg
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Are the forces balanced?
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Will it begin to move? In which direction?
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What force would be needed to stop the object sinking?
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Why can't we float in air?
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- identify the forces on an object and the direction in which they are acting
- demonstrate understanding that forces on a stationary object,
eg upwards and downwards, are equal
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