Re: safe explosions

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From: Raleigh McLemore (raleighmclemore@yahoo.com)
Date: Tue Feb 11 2003 - 09:31:36 PST 

Message-ID: <20030211173136.51173.qmail@web40209.mail.yahoo.com>
Date: Tue, 11 Feb 2003 09:31:36 -0800 (PST)
From: Raleigh McLemore <raleighmclemore@yahoo.com>
Subject: Re: safe explosions

Same basic problem in the fifth grade.

Have you tried using a blown up balloon, taping some
thin, individual strands of steel wool tightly across
it and running 6-9 volts (the square, "transistor
radio" type batteries work well) through the wire?
This causes the steel wool to incandesce, melt into
"sparklers" and burn through the balloon, with a
satisfying pop. This is a good model of the common
household glass fuse with the steel wool showing what
excessive current will do to insufficent conductor.
If you couple this experiment with making a variable
resister, cut the wood off one side of the pencil
exposing the graphite, and run the circuit through the
graphite at different points you can show the gradual
heating of the steel wool and overload it slowly. Not
quite playing with fire.

My fifth graders never tire of popping film cannnister
rockets, they use baking soda and water, dry ice, etc.
to fire them up. This year a student rigged a film
cannister under a cup, then had her partner put
another, loaded, rocket on top of the cup. The first
rocket shot the cup and the "second stage" rocket into
the air where Mr. Newton came into play and I got hit
by the "second stage" as it tumbled and fired wildly
sideways (I went running around saying, "Did you see
that! Did you see which way the film cannister went
and the film cannister top went??? Opposite!!!! What
could we do to make the second stage more stable?").
With goggles I think minimal danger, but many
opportunites to talk about force and motion.

Actually I think all types of rockets qualify as
"explosions" and stomp rockets are hellafun.

I will not mention the "whoosh bottle" demonstration.

With firm handshake,
Raleigh

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