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Life's Ups and Downs

Topic: 6E Forces in action

Hot air balloons rise and submarines sink but why? Both depend on the principle of upthrust. An Indian textile millionaire reportedly broke the world record for the highest flight in a hot air balloon. The balloon soared to 21,000 metres. Balloonists need to know how to alter the weight of the balloon in order to rise or to fall. Submarines take on water in order to dive and expel it to rise to the surface.

In this activity children learn about upthrust and its effects. They label an explanation of how submarines work. They draw force arrows on a diagram of a hot air balloon and calculate how many children might be lifted.

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