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Imponderables(R): Science (Collins Gem)
By David Feldman HarperCollins Publishers, Inc.
Copyright © 2006 David Feldman
All right reserved. ISBN: 0060898860
Chapter One
Why Do Straws in Drinks Sometimes Sink and Sometimes Rise to the Surface?
The movement of the straw depends upon the liquid in the glass and the composition of the straw itself. The rapidly rising straw phenomenon is usually seen in glasses containing carbonated soft drinks. Reader Richard Williams, a meteorologist at the National Weather Service, explains the phenomenon:
...the rise occurs as carbon dioxide bubbles form on both the outside and inside of the straw. This increases the buoyancy of the straw and it gradually rises out of the liquid.
The gas is under considerable pressure when the drink is first drawn or poured. When that pressure is released the gas forms small bubbles on the sides of the glass and on the straw. As the bubbles grow the straw becomes buoyant enough to "float" higher and higher in the container.
Occasionally, though, a straw will rise in a noncarbonated beverage, and we didn't get a good explanation for this phenomenon until we heard from Roger W. Cappello, president of strawmaker Clear Shield National. We often get asked how our sources react to being confronted with strange questions. The only answer we can give is--it varies. Sure, we like authoritative sources who fawn over us and smother us in data. But we must confess we have a special place inour hearts for folks like Cappello, who make us sweat a little before divulging their secrets. Here is his letter to Imponderables, verbatim, skipping only the obvious pleasantries:
After pondering your question for a while, I decided to toss your letter as I was too busy for this. I later retrieved the letter and decided I would attempt to give you an answer that is slightly technical, mixed with some common sense and some B.S.
First off, I know the action you were referring to had something to do with "specific gravity." Specific gravity, as defined by Webster, is "the rate of the density of a substance to the density of a substance (as pure water) taken as a standard when both densities are obtained by weighing in air."
Straws today are formed from polypropylene, whereas many years ago they were made of polystyrene, before that paper, and before that, wheat shafts.
Assuming water has a specific gravity of 1, polypropylene is .9, and polystyrene is 1.04. A polypropylene straw will float upward in a glass of water, whereas a polystyrene straw will sink. However, a polystyrene straw will float upward in a carbonated drink as the carbonation bubbles attach themselves to the side of the straw, which will help offset the slight specific gravity difference between water and polystyrene.
A polypropylene straw will float higher in a carbonated drink for the same reason. If you put a polypropylene straw in gasoline, and please don't try this, it will sink because the specific gravity of gas is lighter than water.
If you lined up ten glasses of different liquids, all filled to the same level, the straws would most likely float at all different levels due to the different specific gravities of the liquids and the attachment of various numbers of bubbles to the straws.
I really wish you hadn't brought this up as I'm going to lunch now. I think I'll order hot coffee so I can ponder the Imponderables of my business without distraction.
Good luck.
We can use all that good luck you were wishing us. I'm sure you had a productive lunch, too. Anyone willing to share information with us can eat (and sleep) with a clear conscience, knowing that he has led to the enlightenment of his fellow humans.
Submitted by Merrill Perlman of New York, New York.
Continues...
Excerpted from Imponderables(R): Science (Collins Gem) by David Feldman Copyright © 2006 by David Feldman. Excerpted by permission.
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