A Head for Science
This is a good eye catcher for a "first day" demo. If you have a lab bench to "hide behind", even better!
Obtain a Styrofoam head from a local clothing store. They usually have one or two that have been dented or have other slight damage. Using a "naked" hacksaw blade and a pair of gloves, cut out a cavity in the head so that a 400-mL beaker can slide smoothly in and out.
Now paint the head I like bright blue. It looks unusual, and requires no artistic talent.
Half-fill the beaker with acetone and make sure that no traces of the solvent will contact the head as you slip it in the cavity.
Put a baseball cap on the head to hide the rim of the beaker. Cut a hole in the top of the cap to lower the Styrofoam strip through.
Lower a strip of white (low-density) Styrofoam (from as thin a sheet as you can find I use strips 3cm x 4cm x 100 cm) into the acetone. It dissolves quickly, releasing the gas that was used as a blowing agent. Like magic, a one-metre strip collapses into the beaker. When the students say "Do it again", pretend to reach into the head and pull another strip slowly from behind your lab bench. Move it over the head and repeat. (You can dissolve three of those strips in a half-beaker of acetone)
Now you have a messy solution of acetone
and styrene to deal with!
Before you dispose of it, use some of it to glue objects together and explain the basis of "airplane glue". Remove the beaker carefully from the head and store it in a fume hood until you dispose of the materials.
Any tiny spills as you lift the beaker out of the head will result in unwanted styro-brain surgery.
1. Acetone vapors are very flammable. Be sure NO sources of flame are in the classroom. This is especially important because the dissolving Styrofoam releases a lot of gas that will distribute flammable vapors far from the beaker.
2. Because of the release of gases from the beaker, the demonstration should be done with lots of ventilation.
See Flinn Procedure #18a.
The dry solid styrene (and probably, your beaker) may be appropriate for your local landfill.
I use this often in conjunction with the "Liquid Science" demo.
"Many students think that Teachers are
trying to stuff their heads with information"
lower one strip after another into the head.
Then I claim that it's NOT what we are actually trying to do.
Science has Big Ideas that fit together
like the Big Molecules of Starch in the "Liquid
Science" Demo. So they have to try to get into it slowly,
not all at once.
(See that Demo for the rest of the story)
They usually think that I have a hole underneath the head, so for the last part of the last stick, I lift up the head to show that nothing is coming out the bottom.
You can also go from here to the nature of
it IS a Foam, full of gas.
"Why don't we dissolve all that stuff instead of putting it in the landfill?"
This is a good question for students to research.