Plastics: Imagine Life Without Them

Suppose you could step inside a time machine and go back 50 or 100 years. You may easily convince yourself of a day without cars, telephones, and television - maybe even computers - might be kind of fun. Have you thought about the little things, though? Little things are often what is missed the most.

Imagine a day without touching something made of plastic!

People were cleaning their teeth before there was a choice of red, blue, or purple plastic toothbrushes but would you really want one made from metal or wood? Milk and shampoo didn't always come in plastic bottles and that wasn't a problem - unless you fumbled and dropped the glass bottle. What a mess!

The word plastic comes from the Greek word plastikos, meaning "able to be molded." That characteristic, or what scientists call "property," makes plastic perfect for things like action figures and dolls.

What other properties does plastic have that make it a good choice for particular items?

Try these experiments, then use what you learn to list 10 or even 20 items that you think should be made from plastic.

Materials:

• Pieces of aluminum, plastic, and wood at least 12" long, 1" wide and 1/8" thick (rulers will work and perhaps a strip of aluminum guttering)
• Two 6" stacks of books
• A 1 to 2 # canned good item
• A length of 4' string
• A tennis ball
• A small plastic and a paper grocery sack

Place the two stacks of books about 9 inches apart. Lay the aluminum strip across the books, making a level bridge. Lay the string parallel to the strip. Next place the canned good in the middle of the strip. Use the string to measure the deflection (bend) in each strip. Repeat the process with the wood and plastic, then record and discuss what you have observed about the strength and stiffness of each material. Given what you have observed, which material would you choose for your toothbrush handle? And the bristles?

Next soak the tennis ball in a sink of water until it is thoroughly wet. Place it first in the plastic sack and then the paper one, letting it set in each for 5 minutes before shaking each vigorously. Which bag stays dry? Does the water cause the paper to sag and even break? What can you conclude about how each material repels or absorbs water? In which bag would you choose to take home a carton of ice cream?

The information, or data, you've gathered and recorded from your experiments is just what a scientist uses to decide what material to use in an engineering design!