December 29, 2014

Why do your ears hurt underwater or when you drive up in the mountains?  The reason is because of the change in pressure.  This episode explains why that happens.


Episode 13: An Ocean of Air

I’ve done several episodes about pressure.  Barefoot on a Bed of Nails introduces the idea of pressure in a painful way!….and The Vacuum Chamber  shows some cool demos you can do with pressure differences (including making your own mini-pressure chamber from a bottle).

In this episode I explain why air pressure changes with your elevation above sea level.

A little pressure pre-explanation

We all live in an huge ocean and we don’t even realize it (most of the time).  This particular ocean, however, is made of air and not water.  How deep we are in this ocean of air is what determines the air pressure.  If you were to hang out down at the bottom then you would have a lot of air above you and all of that air is heavy.  This would exert a large pressure on your body.  If you were to hang out near the top of this ocean of air then you don’t have very much air above you and so would have a very small pressure on your body.  The same idea is true for water pressure.  In fact, that’s probably an easier place to start anyway…


A fluid is  a substance that flows–so basically a liquid or a gas.  The depth of the fluid at a certain point is the main cause of the pressure at that point.  If you want to explore that more and get a little bit more mathy I recommend this video explanation.  It is by Paul Hewitt, a master lecturer and pioneer of teaching conceptual physics.  We use his textbook in one of my physics classes at school.  I am a big fan of his approach to teaching.

Let me know if you have any questions:)