1. Pressure Changes D. Crowley, 2008

2. Pressure Changes To be able to explain what happens to a diving bell when pressure changes Sunday, May 24, 2015

3. Compression (squashing) Which states can you compress (solid; liquid; gas)? Only gas can be compressed, as it is the only state which has particles far apart, with space to be squashed into

4. Compression Gas particles randomly hit the side wall ½ the space, and the particles will hit the wall 2x as often (pressure doubles) ¼ the space, and the particles will hit the wall 4x as often (pressure quadruples)

5. Pressure The greater the depth, the greater the pressure (the weight of the water above compresses the water below) Pressure = gravity x depth x density Low pressure High pressure

6. The Bends As divers go deeper into the sea, the pressure on their body increases, squashing the lungs (which are full of gas) to a smaller volume Some of this high pressure gas (mainly nitrogen) can dissolve into the blood If the diver surfaces too quickly the gas within the blood expands, producing large bubbles, which can hinder the flow of blood and other bodily processes

7. Diving Bell A diving bell is an airtight chamber, open at the bottom It is lowered underwater to help transport divers deep underwater, or as a rescue device The pressure of the water keeps the air trapped inside the bell so the divers can still breathe

8. Making A Diving Bell 1.Almost fill the bottle with water 2.Make a model diving bell by putting a ball of plasticine onto the end of the syringe 3.Drop the model into the bottle, with the plasticine end downwards 4.If the model sinks completely, take it out and remove some of the plasticine – change the amound of plasticine until the model just floats near the top of the water 5.Fill the bottle completely with water 6.Squeeze the bottle and look at what happens to the syringe diving bell – record what happens

9. Recording findings

11. How It Works The bell is ballast so it stays upright As a diving bell is lowered, increasing pressure from the water compresses the gas in the bell Adding gas keeps the air space the same as the bell descends in the water, as well as refreshing the air - this would become saturated with a toxic level of carbon dioxide and depleted of oxygen by the respiration of the divers if left for too long

12. How It Works As you push on the bottle the air pressure in the bell decreases (the water pressure doesn’t change – it can’t be squashed) The lower pressure makes the bell less buoyant (and more dense) so it sinks When you release the balloon the pressure increases again and it floats back up (now less dense)