Tuesday, November 29, 2011

Oceans: Increasing Pressure with Depth

Students don't always understand that the deeper you go under water, the greater the pressure.  This immense pressure is one of the reasons why so much of the ocean floor is still unexplored. 

Try out this demonstration to help your students visualize the pressure increasing as they travel deeper.

Begin with an empty carton from a half-gallon of milk or OJ.  (A bottle would work too, but it's much more difficult to make the holes). 

You'll also need some masking tape, a large tub in which to collect water and a poking device - I found a skewer worked well for me.

Lay the carton on its side on the table and make a hole near the bottom of the carton.

Make a second hole 1 - 2" above the first hole and a third hole 1 - 2" above the second hole.

Run a strip of masking tape down the carton, covering all three holes.

Fill the carton with water and set it on the table, with a tub to catch the water when it spills out of the holes. 

When you're ready, remove the tape and observe the water flowing out of each hole.

The water coming out of the bottom hole is under the greatest pressure (it has the most water/weight on top of it) and it is pushed out of the carton with much greater force - look how far it shoots out.

The water coming out of the top hole is under little pressure (there's not much pushing on it), so it sort of dribbles out.

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