Floating diver – STEM pressure activity

A floating diver toy depends on buoyancy and an object’s ability to float in water. This STEM activity uses a Cartesian diver to show how pressure can change the size of a bubble.

Safety note: Be sure to explain safety precautions to children. The floating and diving activity uses water. Disclaimer: All information provided on this site is for entertainment and education purposes only. Using any information from thecasabouquet.com is at your own risk.

Instructions for floating diver

Fill a glass or cup with water. You will use this glass to test your floating diver.
Squeeze the bulb on the eyedropper to fill the glass tube with water. How full does it get?
Place the eyedropper in the glass. Does it float? If a lot of it is above the water, you will need to get more water into it. Try holding it upside down so the water goes into the bulb. Now try to get more water into it – holding it under a running faucet might work.
Test your floating diver until most of it is under the top surface of water.
Fill a plastic bottle with water, all the way to the top. Place the diver in the bottle and screw on the cap.
Squeeze the sides of the bottle. What happens? Describe what happens to the air bubble in the eyedropper.

What questions can you answer with the floating and diving toy? Can you make the diver float at different heights in the bottle? Does it work the same in a large bottle and a small bottle? What happens if you fill the diver with colored water? Try this with a ketchup, mustard, or soy sauce packet. How does a whale go up and down in the ocean? A submarine?

Supplies

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An empty plastic bottle (drink or dish soap)
Eyedropper
Drinking glass

More: plastic pipettes, drinking straw, clay or sculpey, hex nut, ballpoint pen cap

What is the science?

Content: buoyancy, ideal gas law

Objects with density lower than water will float. The bubble in the diver changes when pressure is applied to the bubble, changing the density of the diver and causing it to sink.

Resource links

http://www.physics.org/interact/physics-to-go/cartesian-diver/index.html
- A demonstration of a diver made from a straw
http://buggyandbuddy.com/cool-science-kids-make-cartesian-diver/
- Make a diver from a pipette and hex nut from Buggy and Buddy

Let’s talk story

In the 1980s, it was pretty common for cereal to include a toy inside. I got this Tony the Tiger floating diver toy and immediately added him to my stash of physics toys. I wish they would make these available again!

I’ll be looking for comments below, or contact me at lisa [at] thecasabouquet[dot]com.