The author replies to Senkbeil:Dr. Senkbeil has added excellent safety considerations to the milk jug rocket car demonstration. A couple of additional safety comments should be made: - The tunnel-like blast shield will help keep the rocket car from initially tumbling, but may not keep the car from tumbling after leaving the shield.
- It is imperative to make sure that all liquid ethanol is removed from the jug to help prevent it from catching on fire.
I had initially used ethanol in my rocket car but I encountered difficulties with the lower volatility of ethanol compared to methanol (1). It seemed in my hands that the ethanol would not completely volatilize and the film of excess liquid ethanol coating the inside of the jug would continue to burn if not manually blown out. On one occasion this continued burning of an alcohol layer actually melted and burned part of the milk jug in a rather spectacular fire. The damaged jug may be viewed online (accessed Oct 2003). Since then I have opted to use the much smaller quantity of the more volatile methanol. Another type of rocket car that circumvents the whole issue of fire as the basis for propulsion uses the pressure from chemical production of carbon dioxide as a source of thrust. The carbon dioxide is produced by reaction between acids and carbonate salts. We have built a rocket car using a 35-mm film canister attached to a chassis made from LEGO parts and propelled it using water and AlkaSeltzer tablets. This car is shown and described in more detail online (accessed Nov 2003). Literature Cited- Ohe, S. Vapor Pressure Data. (accessed Nov 2003).
|
Citation
