Physics in Action: Pressure in Graduated Cylinder

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Let's check out this really neat demo, which shows the relationship between increased depth below the surface of a fluid and increased pressure. This looks to you like a graduated cylinder, but this is really a funny looking swimming pool, and Igor here is a deep-pool diver. Now we have sent Igor down to clean up the bottom of this pool and it looks like he has completed his job. Igor, yeah you're done. We are going to pull him out very gently, and we are going to ask ourselves what did Igor experience as he went down and as he came up.
Now we know what he should have experienced. We have learned as you go farther below the surface of fluid like this colored water, the pressure increases. And we want to demonstrate this scientifically. We are going to do that in the following way. Now this really is a graduated cylinder. At three points in this graduated cylinder here, here, and here we have drilled holes, which are now covered up with pieces of tape. We are going to pull off the tape from these holes, and we are going to show you that at the points farthest below the surface of this fluid, where we expect the pressure to be greatest, it is going to supply the most oomph to the water, and it is going to cause the water to shoot out at the greatest horizontal velocity. The effect is going to be less dramatic in the middle where the pressure is less and the least at the top where we have the least pressure.
Now we're going to demonstrate this right now, I am going to pull up all three of these pieces of tape, and we are going to see what happens. Keep your eye on the streams of water as they come out. Notice that the pressure, where we expect the pressure to be greatest at the bottom, the fluid does indeed, come out with the greatest horizontal velocity. The velocity is less for this stream over here; and the stream that came out from the top, if you saw it very, very quickly, you saw that it came out with the absolute least velocity among the three. Notice as we continue, this comes out with a greater velocity than this, and if we watch it go on and on, you will see eventually that the stream will of course. But the velocity is always greater for the hole at the bottom than it is for the one at the top. Well let's stop this at the moment, and now make some comments.
This demonstration applies not just to fluids, not just to liquids, but it applies to all fluids. It applies especially to air. Now air is an example of a fluid, as we know. What it tells you that, if we live at the surface at the sea level, where we are farthest below the top of the atmosphere, we expect pressure to be the greatest. We expect it to be less as we go up to higher, higher elevation. For example if you compare the air pressure in New York City which is roughly at sea level, to the air pressure in, let's say Denver, Colorado, which is a mile high, we expect the pressure to be less in Denver, and in fact it is. And the pressure is still less at the top of Mount Everest it is so little in fact that you need special equipment to even survive at that altitude. Even in Denver, you should note, the air pressure is sufficiently different from what it is at sea level that special procedures lets say, have to be used to do ordinary cooking.
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Physics in Action: Pressure in a Graduated Cylinder Page [1 of 1]