Chapter Graphic
 : Wonderful Water
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Approach: Independent  Level: Year 8
Focus: Explain buoyancy and flotation in three situations.
656k
Resources: None

Questions / instructions:
Look at the pictures then answer the questions.

     
% responses
y8

1. Imagine that you have a ball of plasticine. You put it in water and it sinks. Then you shape it into a boat. Now it floats. Why did the ball of plasticine sink but the boat float?

boat shape displaces enough water to hold weight of plasticine
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more spread out so it floats/ water holds it up there
8
because there is air inside it.
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2. Why do things feel lighter when you pick them up under water?

some of the weight is supported by the water displaced
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because water is less dense than air
3
there is less or no gravity under water
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3. Someone holds the ball at the bottom.
    Why does it jump out of the water when they let it go?

Under the water:
ball weighs less than the water displaced
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air in the ball makes it rise
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Above the water:
ball moves upward because of inertia
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ball is going fast when it reaches the surface
3
Commentary:
The concepts involved in these situations were beyond the reach or experience of almost all year 8 students.
 
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