Enquiring into fluids

Activities

Bernoulli effect on a string
Bernoulli ball
Freezing the salt out of water
Hot air balloon
Making a laminar flow
Smoke rings
Atomiser
Blowing around corners
See also
Surface tension bits and pieces
Bubbles and surface tension
Other pages on this site

How to do it

Bernoulli on a string
Make an aerofoil section from paper (flat on the bottom, curved on the top, with a more pronounced curve on the leading edge. Draw a piece of cotton through the section, using the needle. When held in front of a fan, the section will rise up the cotton provided
  1. you have the hole in the right place (trial and error) and
  2. you have a hole that is neither too large or too small.
Not the most convincing demonstration -- unless you get it JUST right!

This will help you understand


Creating a laminar flow
You will need a piece of plastic tubing about 900 mm long, such as a length of 90 mm stormwater pipe, a 90 mm joiner, a 90 degree elbow, some plastic conduit, a hacksaw, an epoxy glue such as "Araldite", and a powerful electric fan (try using a small vacuum cleaner), or several smaller fans like the fans used to cool a computer, which can be bought at electronics stores, or stripped out of superannuated computers, requiring a 12 volt DC power supply.

Cut a piece of 90 mm pipe about 300 - 400 mm long, and fit the joiner to it before packing the joiner with 10 cm lengths of conduit: the exact length is not important, but should be the same for each piece. Stand this up, and fit a second length of pipe about 150 mm long on top. Fit the elbow to the bottom, add the remaining piece of pipe, and fit the fan in this horizontal section. Air is pushed through, and directed into a laminar flow.

Make your own experiment . . .

This will help you understand



The Bernoulli ball in miniature
You will need a ping-pong ball, a drinking straw, a cotton reel, some plasticine, and four nails. Fit the straw to the cotton reel, so it goes through the cotton reel, and use a small amount of plasticine to seal it in place. The straw should just come out of the cotton reel on the other side. Surround the top end of the straw with a pad of plasticine, and stick the four nails into the plasticine to make a stand for the ball. Hold the entire arrangement vertical, place the ball on top and blow gently. The ball should hover above the reel.

This will help you understand


Vortex rings
You will need a coffee tin, or other large tin, a balloon, a drill, a punch or a hole saw, and a pair of scissors. You will also need a source of smoke, such as a piece of oily cotton -- which means fire safety rules need to be carefully observed.

Take the top off the tin, make a hole about 2 cm in diameter in the bottom, then cut the bottom half of the balloon away from the top half. Fit the bottom of the balloon to the tin as a top, and pull it until it is tightly stretched over the tin. Hold the hole in the base of the can over the smoke source, and then turn the can sideways and give the tight rubber diaphragm a gentle tap, followed by a stronger tap.

This will help you understand


A hot air balloon
You will need a suitable hair dryer, a large dry cleaning plastic bag (it has to be very light), and some small rubber bands.

This has to be done fairly carefully, so that the plastic does not melt. Use a rubber band to seal the top of the bag, where there are often holes. Put the bottom of the bag over a hair dryer, and attach the bag around the nozzle with a rubber band. Blow hot air into the bag while somebody holds the top up out of the way. When the bag is fairly full, pull the bag off the dryer, leaving the rubber band in place to hold the bottom mostly shut, and let go.

This will help you understand


Fresh water from salt -- the cold way
Fresh water is a coming problem for the world. Most of the world's fresh water is locked up in polar ice caps or as ground water, so the easy way to get more fresh water is to get it from sea water. The obvious way to get the fresh water is to distill it off, but there is another way. To explore this second method, you need a plastic dish (like an ice cream container), a freezer, and a cloth.

All you need to do is put your salt water in the plastic dish in the freezer, and wait until an icy slush forms. As ice crystals form, there is no room in the crystal structure for sodium ions or chloride ions, so the salt is excluded, and the remaining water becomes saturated brine.

At this time, you need to scoop off the ice slush, which will have a coating of brine. If you squeeze the slush in a cloth, you will get most of the brine to come off, leaving something close to pure ice. If you melt this ice into a fresh container and repeat the process a second or even a third time, you can get remarkably fresh water.

This will help you understand


A simple atomiser
This is just about as simple as it looks. Cut a drinking straw almost through, like this, about three quarters of the way along. Put the short end into a glass of water and blow from the other end.

Then sit down and write me a rude letter asking why I didn't warn you to try this outside :-)

This will help you understand why it made such a mess


You can blow around corners!
Light a candle and put a cylindrical container in front of it (something like a full drink can or a salt package). Take a deep breath and blow against the far side of the container, keeping your mouth level with the flame of the candle. Can you blow out the candle? Try it and see what happens.

This will help you understand Back to the index



And now for some help

This file is http://www.ozemail.com.au/~macinnis/scifun/fluids.htm, first created some time in 1997. Last recorded revision (well I get lazy and forget sometimes!) was on July 12, 2001.
Worried about copyright? You need to go look at my fine print . Well, maybe you don't after you read the next paragraph, but do it anyhow . . .and to see some more ideas, look at the start of that same page
©The author of this work is Peter Macinnis -- macinnis@ozemail.com.au , who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. Any non-profit educational or home use is completely acceptable without let or hindrance. Copies of this whole file or site may be made and stored or printed for personal or educational use. The work used here derives from on-going research and development which will one day lead to a book on brain food ideas.
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