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Absorbency: Stuff It!


Today's Snack: Toast two pieces of bread, butter lightly, slice on the diagonal, and dip them into a nice cup of hot cocoa made with milk. The toasted bread absorbs the cocoa, and in a delightful but unscientific way, seems to make both toast and cocoa taste even better!






Bag of cotton balls


Cup measure

Small glass or jigger (holding less than one cup)



First, fill the small glass with water up to about one-fourth inch of the top. Pour into the one-cup measure to see how many ounces are in the small glass. Then pour the water back into the glass, and dry the cup measure.


Next, line up the cotton balls along the ruler and record how many inches the line of cotton balls form.


Next, fill the dried-out cup measure lightly with cotton balls. Do not press down; just place the cotton balls in the cup gently. Count how many cotton balls filled the cup measure to the top.


Then estimate how many cotton balls you could get into the small glass of water before the water spills over the top. Many students will guess two or three cotton balls.


Finally, start pushing the cotton balls into the small glass of water. Press each one down firmly with your fingers to make room for others.


How many could you squeeze into that glass? Are you surprised?


Here's an explanation:


Cotton comes from a plant. It is the most universal fiber known, used around the world to make fabric and all kinds of things. The fibers in cotton are mostly made up of cellulose. That's a complex carbohydrate that is part of many plants. Each individual cotton fiber is about one inch long and only 10 to 20 microns thick. That is very, very slender - only about 1/10th as wide as a strand of your hair!


Because of these incredibly slender fibers, each fluffy cotton ball actually has tons and tons of air in it. A cotton ball is mostly fluff - empty space.


No wonder, then, when the water soaks into the cotton fluff, the cotton ball is compressed and its volume - the amount of space it takes up - is greatly reduced.


Because it has so much air around it, cotton fiber is tremendously absorbent. Can you think of reasons why that would be good? (Diapers, rags, bandages, etc.)


After this lesson, please squeeze out the cotton balls and lay them out to dry for reuse. Note that they'll never be as fluffy again, even when completely dry. But they can still be put to good use.


By Susan Darst Williams www.AfterSchoolTreats.com Experiments 04 2009

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