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Plastilina Buoyancy Investigation

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Plastilina Buoyancy Investigation

Can the same piece of plastilina sink as a ball but float as a boat? Try the investigation with an adult. You will need a lump of plastilina, a clear tub of water, and small counters or marbles. Keep water away from electrical items, and dry up spills.

Set up and test

1. Make a ball from the plastilina and place it gently in the water. Record what happens. 2. Take it out and dry it. Shape the same plastilina into a boat with raised sides. 3. Place the boat gently on the water. Add counters one at a time until it sinks. Count the counters. Keep the tub on a steady surface.

1.Before testing, predict what will happen to the plastilina ball in the tub of water.

It will float on the surface.
It will sink to the bottom.
It will stay halfway down.

2.Test the ball. What happened? Write or draw your observation.

3.Draw the plastilina boat you tested. Show the waterline and the counters in or on it.

4.When you placed the boat on the water, did it float or sink? Record what happened in your test.

5.Add counters one at a time. How many did your boat carry before it sank? Write the number and describe what happened.

6.Which statement best explains why the boat shape can float even though the plastilina ball sinks?

Shaping the plastilina makes it lighter.
The boat shape takes up more space and pushes more water aside before water comes over its sides.
The water holds up only objects that are wide.
The boat shape changes the plastilina into a different material.

7.Circle the things that should stay the same to make this a fair test: the amount of plastilina, the colour of the tub, the water used, the shape of the plastilina.

8.A friend says, “The boat floated because the plastilina became lighter.” Is this a good explanation? Explain your answer using what happened in the test.

9.A metal ship is much heavier than a plastilina boat, but it can still float. Which idea from this investigation helps explain why?

10.Your first boat sank after three counters. Name one change you could try to help a new boat carry more counters, and say why it might help.