Pressure

Today students began Unit 1 on Oceanography. First we discussed the names of the five oceans - yes there are 5! The fifth one was added in 2000 and is called the Southern Ocean. It extends around Antartica and is found below the 60*S latitude.

We discussed the salinity of the ocean and where the salt comes from. The salinity of the ocean is 35ppt, very similar to the amount of salt in our blood.

One class discussed the pH of the ocean, the other will discuss it tomorrow. The key thing to know about ocean water is that it is not neutral! It is slightly basic, about 8, because of calcium carbonate, one of the two main salts found in seawater.

We finished notes by discussing pressure. Pressure increases underwater and with depth because there is more matter above you the deeper you go. Water is more dense than air though, so a change of 10 meters increases the pressure by one atmosphere.

Scientists are a silly bunch and are sometimes artistic. There are few submersibles that go down that are not accompanied by a styrofoam wig head. As the submersible descends, the pressure increases so much that the air is squeezed out of the styrofoam and the head shrinks.

Ms J has some styrofoam cups (donated by a former student) that went 12,000 feet down on a submarine that are very similar. They used to be 12oz cups and now they are only about 4 inches high.

Students finished the day with a pressure lab looking at cups with holes in them. When the cups are filled with water the different holes shoot water out at different rates. Generally the hole at the bottom of the cup shoots the furthest because it is under the most pressure. The hole at the top of the cup barely shoots, and not for long, because there is way less pressure pushing on it.