Diver in a bottle

Make your own deep sea diver in a bottle! This little diver will go up and down when you want it too. It’s a great way to trick friends and family, you’ll be able to control the diver, to make it go up and down whenever you want! If you’re careful no one will guess how you’re doing it.

The things you need

  • A plastic bottle (an empty soft drink bottle)
  • A pen-cap (one with a sealed top and no holes apart from the one for the pen!)
  • Plasticine or Blue-Tack
  • A jar or wide glass full of water

Things you might like to have!

  • A green plastic bag, and little rocks
  • Texta’s (water-proof ones)
Diver  in a bottle
A pen-cap diver in a bottle.

How to make your diver

Weighting the pen cap
Get the weight right on the pen-cap.
  1. First you must add weight to your diver (the pen-cap) with blue tack or plasticine. Put blobs on the arm of the pen-cap (but don’t block the hole at the bottom). Then test your diver in a bowl full of water. Drop the pen-cap in, so it catches a bubble of air and get it to float just on the surface (see the diagram —->).
  2. Now fill up your plastic bottle nearly to the top.
  3. Drop in your diver (remember to catch a bubble of air in it!)
  4. Screw the lid on your bottle!
  5. Squeeze on your bottle and watch the diver sink. Let go of the bottle and watch the diver come back again!

Decorate your dive tank

1. Make some sea weed. Cut green plastic garbage bags into short strips and weigh the plastic strips down with paper clips or plasticine blobs.
2. Colour in your bottle with textas.
3. Put several divers in at once, they won’t all move at the same time!
4. Try using a glass eye dropper or a clear pen-cap. You’ll be able to see the bubble on the inside. It will get smaller and bigger as you squeeze and let go!


QUESTION? What if my diver sinks and doesn’t come up?

ANSWER: Your diver was a bit too heavy. Take some weight off and test your diver again.

QUESTION? I squeeze really hard but my diver doesn’t sink at all!

ANSWER: Your diver may need a bit more weight OR you may have too much air in the bottle. Try adding more water if the bottle isn’t full.

Why does it do this?

Your pen-cap diver has a little bubble of air inside. When you squeeze on the bottle you are making the air in the bottle smaller. The water doesn’t get any smaller, (it’s impossible to squeeze water and make it shrink). So the bubble in the pen-cap shrinks. The whole pen-cap loses bouyancy and so it sinks.

An experiment you can try

Next time you go for a swim try to hold your breath and sit on the bottom of the pool. Its really hard to do! If your lungs are full, you’ll probably bob around close to the top of the water.

The only way you’ll be able to sit on the bottom, is if you blow out most of your breath. You won’t be able to stay down long, but you’ll definitely sink as you blow out bubbles. The first time you try, blow out as much air as you can before you go under.

Some people will find it harder to sink than others. That’s because some people have more body fat. Muscle and bone help you sink, but fat helps you float. Women have more body fat than men do and so women usually find it easier to float!

It doesn’t matter how big or small you are. What’s important is how much of you is made of fat compared to muscle or bone. Someone who is big may have heavy bones. So even though they don’t look skinny they may still be able to sink when they want to!

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