Mystery #4Tier 2-3water / pressure / density
How does a heavy metal submarine choose to sink, then float back up?
A submarine is built from thousands of tonnes of metal, yet it can rest on the surface like a duck one minute and slip deep underwater the next, then rise again exactly when it chooses. Most things either float or sink and are stuck that way forever. How does a submarine get to pick?
Your guess
What's your hunch: how does the submarine make itself sink or rise?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
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