5 Minute STEM Activity 14 - The Diver

This project helps you to understand some really complicated Scientific principles, including pressure, volume and buoyancy - but it is really easy and it's fun... And you don't need anything special.

The Diver
Neutral Buoyancy

EQUIPMENT:
A water bottle with a screw top lid.
Water
Small square interlocking construction bricks - 4 stud LEGO or similar.
Sticky Tack or Dough

Instructions:

1. Fill the bottle with water, almost completely to the top. If you are working somewhere indoors then it might be best to work on a tray, or in the sink (with the plug in so you don't lose anything small down the plughole). This can get a little splashy at first.

2. Make a diver. It needs to have air trapped inside, so stack up bricks together. We started with 4, but it was too many, so we thought 3 was better. The bricks trap the air, but they don't form a completely watertight seal.

3. Add a weight at the bottom of the diver. This will keep him upright and although we need our diver to have BUOYANCY and float, we also need the diver to be able to sink, so he needs to be a little heavier. You are trying to make him so heavy that he just floats at or near the top of the water. Add more sticky tack until he seems right. My diver is called Bob.

4. Check the buoyancy of your diver by screwing the lid onto the bottle tightly.

5. Give the bottle a squeeze.

6. If the diver is heavy enough then he will sink as you squeeze the bottle. This is because you have increased the pressure inside the bottle. Let go of the bottle and he will rise. If he doesn't sink, add more sticky tack. If he doesn't float back up, take a little bit away.

7. Your challenge is now to get the diver to sit somewhere in the middle of the bottle. Not at the top, or the bottom. Congratulations! You have NEUTRAL BUOYANCY. Real divers also need to be able to swim under the water, but not sink to the bottom.

There is lots of science behind this, but basically the reason the diver sinks is air is less dense than water. It's easier to squash air than water, and although you can't see it, water even pushes it's way in between your bricks and shoves in with the air. When you stop squeezing the bottle, the air can spread out again and push the water back out. When you take your bricks apart, you may find a drop or two of water inside as a leftover clue...

Why do you think this is important to real divers? Why is it especially important to deep sea divers? Can you think of a watercraft that relies on this process to go up and down in the water?

If you are older and want to find out more, try Googling:
Density
Buoyancy
Mass
Cartesian Diver

You can find all of the 5 Minute STEM Activities here...