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← Explorers EngineeringHull design20 minutesStd 3–5

Foil Boat Cargo Test

✨ The same square of foil carries three coins as a deep cup and thirty as a wide flat barge.

A deep narrow foil boat holding three coins with a small up-push arrow beside a wide flat barge holding twelve coins with a much bigger up-push arrow, showing the larger volume of water pushed aside.
How it works

🧰 You need

  • aluminium foil
  • a bowl of water
  • a pile of identical coins
  • a ruler
  • a paper towel

⚠️ Foil edges can be sharp, so ask an adult to help with the cutting.

👀 What you will see

A wide flat hull sits low but takes many more coins than a deep narrow one. The boat sinks suddenly, the moment one side dips under and water pours in. Coins piled on one side tip the boat long before it is really full.

🧪 Do it

  1. Cut three equal squares of foil, about fifteen centimetres each.
  2. Shape the first into a deep narrow cup, the second into a wide flat barge and the third into any design you like.
  3. Float the first boat and add coins one at a time, spreading them out.
  4. Count the coins it held just before water came in, then dry the boat.
  5. Test the other two the same way and record all three counts.
  6. Redesign your best boat and try to beat your record.

💡 Why it happens

A boat floats while the water it pushes out of the way weighs as much as the boat and its cargo together, and that upward push is called upthrust. A wide hull pushes aside a lot of water for only a small drop in level, so it can take more cargo before the sides go under. Once water comes over the edge, the trapped water adds weight without adding any new upthrust, so the boat sinks quickly. Spreading the coins keeps the hull level, which is why real ships care about load distribution.

🔁 Now try this

Keep the hull shape the same but double the size of the foil square, and see whether the coin count doubles too.

🤔 Think about it

Why do cargo ships have a load line painted on the side of the hull?

🧘 Ask the Acharya

“Why do cargo ships have a load line painted on the side of the hull?” — ask him and he will explain it from your own chapters.

Ask Guru →

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