This Week's Experiment - #280 Viscosity
I was so busy having fun that I put off working on this week's experiment. I
had several ideas bubbling around in my brain, but nothing quite came
together. Then, as I often do when I am looking for an idea, I picked up the
first thing I saw and began playing with it. It happened to be a bottle of
liquid soap. I turned it over and watched as the bubble rose slowly through
the thick liquid. I knew that I had this week's experiment. You will need:
several clear bottles of liquid. You can use cooking oil, vinegar, shampoo,
honey, window cleaner, cough syrup, or any other liquid that comes in a clear
bottle.
We are going to test the different liquids for their viscosity. What in the
world is viscosity? It is a liquid's resistance to flowing. If a liquid has
a low viscosity then it flows very easily, like water. If it has a high
viscosity then it flows very slowly, like honey.
One way to test viscosity is to drop objects into the liquid and time how
long it takes for them to fall to the bottom. You could do this test by
dropping marbles or small stones into each bottle of liquid, but whoever does
the cooking at your house would not be pleased to find rocks in the bottles
of oil, honey, etc. A much neater way to test viscosity is to use rising air
bubbles instead of falling rocks.
First, check the top of each container, to be sure that it is securely in
place. This is the voice of experience talking, as the top for my liquid
soap was not very secure during my first test. Turn the bottle upside down
and watch what happens. You should see one or more air bubbles rising
through the liquid. Depending on which liquid you used, it may have moved
quickly or slowly. Try other liquids and compare the speed of the rising
bubbles.
As you test different liquids, arrange them in order of their viscosity
with the highest viscosity at one end and the lowest at the other. You can
even make your own viscosity chart, allowing you to quickly rate the
viscosity of each new liquid.
Viscosity is very important. Motor oil commercials talk about viscosity
frequently. If an oil is not viscous enough, then it will not lubricate the
engine enough. This lets friction heat the engine and possibly damage it.
If the oil is too viscous, then it is difficult for the engine parts to move,
which is also not a good thing. Viscosity changes with temperature, so motor
oils must keep the right viscosity in very hot and very cold weather.
Viscosity is also important in foods. Each gravy or sauce has its own proper
viscosity. Imagine spaghetti sauce as thin as water or soup as thick as
honey. Different gravies have different viscosities. The "Red Eyed" gravy
made from good, southern, country ham is almost as fluid as water, while some
white gravies are much thicker than molasses. Interestingly, they both taste
wonderful over fresh made biscuits. A stick of butter can easily show you
how viscosity changes with temperature. As with motor oil, the warmer the
butter gets, the lower its viscosity is. Just be sure to remember that
butter is MUCH better on biscuits than motor oil. You can get the opposite
result by pouring hot fudge sauce onto very cold ice cream. You can actually
see the fudge sauce get thicker and thicker as it is chilled by the ice
cream. Don't take my word for it. That is one experiment that you
definitely will want to try for yourself.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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