Pressure

Pressure is the weight of particles above you and increases with depth in water. Right now there is one atmosphere of pressure squeezing on all of us, but we are used to it, so we don't notice the difference. We may notice our ears popping when driving over Shenandoah or flying in an airplane when pressure decreases.

Water is 800 times more dense than air, so underwater, pressure increases dramatically. Pressure increases one atmosphere with every ten feet of depth, so all you need to do is dive down the deep end of the pool and you will feel an increase in pressure to two atmospheres (one for the water, and one for the air)

Scientists think it is funny to take styrofoam deep into the ocean because the pressure underwater will squeeze the air out of the styrofoam and "shrink it." Really it is just compressed and more dense. Here is a photo of what happens to styrofoam wig-heads and cups when taken down a few thousand feet, a change of several atmospheres of pressure. 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.

We did a quick demo lab with plastic cups and water to demonstrate how pressure increases with depth.