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Submarine engineer

This activity looks at some of work of a submarine engineer. A submarine engineer needs to keep the submarine operational and safe, from the life support systems to the electronics and the buoyancy systems. Keeping the submarine at the right depth is essential for submarine operations. This is done using the buoyancy control system, which change the balance of air and water in the ballast tanks. More water and the submersible sinks. More air and it rises.

Ages 8+

15+ minutes

You will learn about the principles of buoyancy and especially neutral buoyancy in this task. Divers, submersibles and submarines alter the air levels in their buoyancy systems to change their density. In this challenge, you will need to create a neutrally buoyant pen lid submarine!

Activity steps

  1. Remove any labels from your bottle so that you can see what is happening.
  2. Fill the bottle to the very top with water. It’s probably best to do this activity with the bottle standing in your kitchen sink, as there are likely to be some small spills.
  3. Fix a small piece of modeling clay to the end of the point on the pen lid. Start with quite a small piece as you can more easily add some more. Retrieving the pen lid from the bottom of the bottle is slightly trickier.
  4. Put the pen lid into the bottle, modeling clay end first. It should just barely float, i.e. about 10cm from the top of the bottle.
  5. If the lid floats too much, ask an adult to squeeze the sides of the bottle gently, until there is enough of the pen top poking out to grab a hold of. You can then add a little more modelling clay to help it sink a little.
  6. If the pen lid sinks to the bottom, you will need to retrieve the pen lid from the bottom of the bottle and take off a little modeling clay. The best way of retrieving the pen lid is for an adult to place a thumb over the opening, turn the bottle upside down, and then remove their thumb for just long enough for the pen lid to come out.
  7. Now screw on the bottle cap nice and tight. Remember to top up the water bottle if you have lost any water getting the amount of modeling clay right.
  8. Now to see if you can make your pen lid submarine rise and fall. Squeeze the sides of the bottle hard. This should make the lid sink. If you stop squeezing, the lid will rise again.
  9. Your challenge is to apply just the right amount of pressure to make the pen lid float in the middle of the bottle.

More ideas

Can you experiment with different factors that might affect how the pen lid floats and sinks? Does the size of the bottle make any difference or how full it is with water? Why might this be the case?

Safety guidance

  • This activity is best performed with the bottle placed in a sink.
  • If a younger child is standing on a stool, make sure it is stable.
  • A safer alternative for smaller children would be to do this activity outside.

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