Science Smarts: An experiment in buoyancy… Happy Canada Day!

By Patty Rooks on July 3, 2021.

It was great to see some familiar faces out at the Canada Day celebration this week. Being able to share our love of science with the community is always a welcome opportunity for Praxis! Of course, a BIG thank you needs to be extended to all of the volunteers that gave up their time and endured the heat on July 1 – we could not do what we do what we do without the generosity of our volunteers. All of our volunteers are eager to share their love and passion for science and I hope when you visited our booth you were able to take away a fun activity. If you missed out on some of our activities, do not fear, here is one you can do at home with some simple materials you likely have on hand. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

empty 500 mL water/pop bottle with a lid

water

medicine dropper/pipette

brass hex nut

Procedure

1. Fill the water bottle almost full of water. Set aside.

2. Place the brass hex nut on the pipette. Push it all the way up to the top just underneath the bulb. Make sure it is going to stay in place.

3. This is the hardest part of the entire experiment , I believe. Squeeze the bulb of the pipette and fill it about ¾ full of water. Place the pipette in the water bottle. You want the pipette to float freely in the water. If it sinks to the bottom, remove the pipette and squeeze out a bit of water and try again until it floats in the water. Be patient – you likely will not get it the first time.

4. Put the lid on the water bottle.

5. Squeeze the water bottle and let it go.

6. Observe what happens.

What is going on?

This experiment demonstrates the scientific principle of buoyancy. When you squeeze the bottle, the diver should sink and when you release the sides, the diver should float to the top. There is just enough air in the Cartesian diver to make it positively buoyant. This allows the Cartesian diver to float on the surface of the water.

There is a great deal of science going on in this experiment, but I do want to keep it simple. Simply put, when you squeeze the bottle, the pressure in the bottle is increased, therefore the volume of air trapped inside the Cartesian diver decreases. As the volume of air decreases, water is taken up into the Cartesian diver which increases the density of the Cartesian diver so it sinks.

Patty Rooks, Senior Scientific Consultant PRAXIS, “Connecting Science To The Community”. Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. Visit us at: #12 826 11 Street S. E., Medicine Hat, Alberta, T1A 1T7 Phone: 403-527-5365, email: praxis@praxismh.ca.

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