- Present pupils with floating objects which they can push down to feel the upthrust pushing up. Extend the range of objects and ask pupils to predict which will float, and to weigh them in air and immersed in water. Compile a table of results and ask pupils to identify patterns and draw conclusions from these. Ask pupils to record their results and explanations,
eg by annotated drawings showing the forces acting on the objects. Discuss pupils' ideas with them, referring to the work of Archimedes. Encourage generalisations,
eg light for size, and show how to calculate density. Displacement of water can be used to measure volume (refer again to Archimedes).
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- state that all the objects weigh less in water than in air
- explain their observations in terms of an upward force from the water 'cancelling out' some of the downward force of the weight
- recognise that objects which float show a zero weight reading
- state that an object will float in water if it is less dense than water
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