Message-Id: <3.0.5.32.19980728111111.007d3a50@isaac.exploratorium.edu>
Date: Tue, 28 Jul 1998 11:11:11 -0700
To: pinhole
From: Eric Muller <emuller@exploratorium.edu>
Subject: re: CO2 bottle cars
Dear Mary,
I originally got the idea for soda bottle cars from an article I read
several years ago in "The Science Teacher" magazine entitled, "Soda Bottle
Boating," but I adjusted it for land lubbers.
In a nutshell (or a 2 litter bottle) - When baking soda and vinegar react,
one of the products is CO2. If you make a small hole in a 2-litter bottle,
combine the ingredients and cap it, extreme pressure will build up.
If only gas, escapes the car won't travel too far. If you position the
bottle so that it forces out the vinegar (or extra water- see materials
below) it will go zooming.
Hints:
If you just throw baking soda into a 2-litter bottle with vinegar in it,
the reaction happens so fast that most of the gas escapes before you can
cap the bottle. One thing I do is wrap the baking soda in a piece of paper
and jam in into the bottle.
A design where the bottle is tilted at an angle and the hole is positioned
in the rear, well below the level of the liquid works best. This allows
forward motion and allows the gas to force the vinegar (and/or water) out
the bottle.
A great feature that my kids came up with was to replace the standard cap
with a pull/pour spout (the kind of cap on bottled water and dishing
washing liquid). This lets the pressure build, when it's high enough the
spout pops open and the car goes flying.
Materials:
Goggles - safety
Old clothes - safety
Must include a 2 litter bottle as the reaction chamber
Maximum of two tablespoons of baking soda
As much vinegar as they want
As much water as they want
Any type of chassis design, but it can't include model/toy car parts.
When I did this event with my students, I never showed them all the
tricks…they had to figure it out on their own. I showed them the reaction
of baking soda and vinegar. I also showed them how a water rocket (toy
store variety) flies if it only shots out high-pressure air vs. water.
I hope this helps!
Eric Muller
Teacher-In-Residence
Exploratorium Teacher Institute
3601 Lyon St.
San Francisco, CA 94123
emuller@exploratorium.edu
415-561-0313