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Buoyancy and Submarines in Mr. Conlan’s Class!

This week we have been reading about submarines in English so we decided to do a few Science experiments exploring buoyancy and flotation.

Our first experiment was to make a Cartesian Diver. This fantastic experiment demonstrates how compressed (squeezed) air becomes more dense. The diver sinks to the bottom when the bottle is squeezed because the compressed air inside it is more dense than the water!  We added plenty of salt to the water and tried the experiment a second time.  Salt makes water more dense so we had to squeeze much harder to sink the diver!

Our next experiment was to build a submarine! We learned that the submarine was invented by an Irishman named John Holland. While we couldn’t recreate his famous “Fenian Ram” of 1900 we could demonstrate how submarines work using a plastic bottle.

Submarines dive by filling ballast tanks with water. They rise by pumping out the water and filling the ballast tanks with air. The air is less dense than the water so the submarine becomes more buoyant and rises to the surface. In our experiment the water fills the bottle through holes in the bottom. The coins keep the bottle stable so the holes stay at the bottom.  As the bottle fills with water it sinks. We then blow through the straw to pump the water out of the bottle and fill it with air. This causes the bottle to rise! UP SHE GOES!!!