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1. Demonstrating the effect of centrifugal force
The equipment required for this demonstration is simple: a
plastic jar (approximately 8 oz. volume) or cup with a screw-on
lid, a piece of string , a couple of elastics. The jar and
lid is easily found in a chemical lab. If you do not have
access to one, you'll have to scrounge something up. Wrap
the elastics around the cup and tie the string to the elastic.
Let er rip, er let er fly, actually let er twirl. The fluid
of course should stay in the bottom even when the glass is
upside down. Do this first with the lid on, some smart aleck
should say: "Well of course you got a lid on". That's
when you take the lid off and do the experiment again. Works
great.
To prove that the fluid is pressurized, make a small hole
in the bottom of the cup with a needle. The hole should be
small enough that the fluid does not drip through when the
cup is motionless. Twirl away, and behold the spray, wonderful
proof that the fluid is pressurized by centrifugal force.
Try it, it works.
2. Make a siphon
Get some aquarium tubing and make a siphon. Great way to talk
about negative pressure.
3. Do the real thing
Get a small aquarium pump and some tubing and transfer water
from one container to another. I recommend the Powerhead MODEL
Pro 2. You can demonstrate the importance of the elevation of
the outlet point. If the outlet point is raised, the Total Head
of the pump is changed and the flow will diminish. Exactly as
one would predict from a typical centrifugal pump. Take a few
measurements and plot a performance curve. The shut-off head
is easily determined by raising the tube until the flow stops,
measure the height from the liquid level at the suction to the
top of the fluid column. Voila!: Shut-off head.
4. Non-Newtonian fluids
Because of their weird behavior non-Newtonian fluids make for
interesting experiments. Mix a solution of cornstarch and water
(1 part water 2 parts cornstarch) into a large bowl. The viscosity
of this solution depends on the rate of shear or in other words
when you move this solution rapidly it stiffens remarkably.
This is known as pseudoplastic behavior. Try throwing the solution
at someone by moving the bowl rapidly, the solution sticks to
the bowl. Great effect.
If you know any interesting experiment with fluids, drop
me a line.
5. Pool Party Time
Here's something fun, and just might be a little unexpected.
The idea is courtesy of Chris Dundorf of Barrington, New Hampshire.
Get a hold of some ?"diameter PVC tube approximately 3
to 4 feet long. Cover the top of the tube with your thumb and
leave the other end open. Move the tube up and down in the water.
Use your thumb to control the air pressure within the tube.
Leave your thumb off at the appropriate moment, I'm sure you'll
figure out when, and you will get a very nice spray of water.
Fascinating, n'est-ce pas? All that with a simple piece of tube.
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