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You will need:

• A tub, bath or sink full of water
• Plasticine/modelling clay

Start off by just dropping a lump of modelling clay into the water. It will sink – but, using the same amount, can you model it into a shape which will float? Try making different designs of boat.

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You can try this activity with lots of other materials. For instance, if you drop a potato into water, it will sink, but how could you make it float?

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What makes things float?
Your model boat needs to be less dense that the water. Density is a scientific term, referring to how heavy something is in relation to its size. You can reduce an object’s density by filling it with air – and the designs which work the best for boats are shapes which trap a lot of air.

You will need:

• 1 piece of A4 paper
• 4 paperclips
• Lots of marbles!
• A tub, bath or sink full of water

In this activity, Maria Rossini set Dick and Dom a challenge (originally from the British Science Association). Using one piece of A4 paper, and four paperclips, they had to create a boat that would not only float, but which would carry as many marbles as possible before sinking. Try it for yourself! Can you beat Dom and Will’s boat, which was able to hold a whopping 76 marbles?

Make your own mini-submarines.

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You will need:

• A ballpoint pen with a clear body (so you can see what’s happening)
• A 1.5 litre bottle
• 5-8 paperclips

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Fill the bottle with water, and keep the lid to hand. Then, take the ballpoint pen, and remove the ink, so you are left with a clear plastic tube with a stopper at the top. Drop it into the bottle of water. It should float. Now, take it out of the bottle, and slide 5 or 6 paperclips onto the bottom of the tube. Put it back in the bottle. You need the pen to be just floating – if you add too many paperclips, it will sink. If it’s bobbing too much, add more paperclips.
Now, put the lid back onto the bottle, with the pen still inside.Ìý Squeeze the bottle. The pen should sink. When you let go, it should rise back to the top – just like a submarine!

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What’s happening?
Watch what happens as you squeeze. The water will enter the tube of the pen, and as it fills up, it sinks. When you let go of the bottle, the air which had been squashed in the tube of the pen is able to expand again, and the pen will float. A real submarine works in exactly the same way. It contains tanks which can be filled with water to make it sink, or pumped full of air to make the submarine rise to the surface again.