Sink or Float?

Some objects sink and some float. Can you design one that does both, like a submarine?

What you will need:

  • One or more plastic film canisters* for your “submarine(s)”
    *You may get empty film canisters from many local photofinishing locations that process film, and if you have a choice, the clear-whitish ones let you see what’s going on inside!
  • 2 liter soda bottle with the top third cut off to hold your “ocean”
  • Water
  • Several Alka-Seltzer® type of fizzy tablets
  • Handful of pennies
  • Scissors

Here’s what to do:

Carefully, make a small hole on the lid of the film canister with the pointy ends of a pair of scissors. (Adults help younger kids). Fill up your ocean two-thirds of the way with water and you’re ready to go diving!

Take it further:

  • How can you make your submarine sink to the bottom of the ocean?
  • What is the fewest number of pennies you can add to get it barely sink?
  • What happens when you now add a piece of a fizzy tablet to your submarine and close the lid? It may splash a bit!
  • Does the amount of water or fizzy tablet make a difference in the action of your submarine?
  • How can you get your submarine to sink, and then slowly rise to the surface two, five, or ten seconds later?
  • Does it matter how your submarine lies on the ocean floor for it to be able to float back up?
  • Does the size of the hole have an impact on the way the submarines behave?
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