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The upthrust on a toy figure placed in fresh water is compared with one placed in saltwater. Femi investigates why the model floats in brine and sinks in the fresh water. She collects the water displaced by the model in both types of water, and measures this volume against the weight of the model.
This clip is from:
First broadcast:
17 May 2007

Classroom Ideas

As a follow-up activity, fill a gas jar or other vessel with a straight lip completely to the top and then ask pupils to predict how much salt can be added before the beaker overflows. Demonstrate by adding salt one spatula at a time to see which prediction is correct. Demonstrate on a balance to show brine is heavier and therefore denser than fresh water. Ask pupils to draw particle diagrams or write an explanation as to where the salt goes in the full container.