Praxis: The science of scuba

By Medicine Hat News on July 29, 2017.

I don’t know about you, but a great way to cool off when the temperatures are soaring outside is to get in the water. Well, if you know me, swimming is great, but how about scuba diving. If you are properly trained, this can be a great way to keep cool in the summer around here. Scuba diving in southern Alberta? You bet, there is a lot to explore in the many lakes we have right here surrounding Medicine Hat. You do not have to be in a tropical location to learn about what is under water — it is a fascinating world just waiting to be discovered. If you are not too sure about scuba diving start small and make some Cartesian divers with me this week. 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 part is a bit tricky. Squeeze the bulb of the pipette and fill it about 3/4 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.

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 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.

I often do this experiment with students when I talk about buoyancy with them. Buoyancy is not only important in this experiment, but also when you scuba dive. You want the pipette to be buoyant and float in the water before you make it dive to the bottom of the bottle.

Scuba divers use special equipment such as weights, diving suits and buoyancy compensators to control their buoyancy. I use weights so that I am negatively buoyant and sink; I can then adjust my buoyancy compensator by adjusting the volume of gas in the bladder (by adding or dumping air), which is taken from my air tank or mouth.

Do not forget about our Summer Science Camps in partnership with Medicine Hat College Continuing Studies. Visit their website at http://www.mhc.ab.ca/continuingstudies for more information.

Patty Rooks is senior scientific consultant at 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.

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