Ethanol Alcohol Rocket, 1N22.60

Topic and Concept:

1N22. Linear Momentum, Rockets

Location:

• Cabinet: Mechanic (ME)

• Bay: (A3)

• Shelf: "T"

Thomas(Tom) Lovell (1946-2005), Lighting the Rocket for one of our Wonders of Physics Shows. He was our MC since the start of the WOP shows in 1986.

Abstract:

A 5 gallon water jug is shot about 20' across the stage with a 3'-6' flame to show propulsion of a rocket using ethanol as fuel. This demo does have performance failure rate of about 10%.

Important Setup Notes:

• Make sure that there is AT LEAST 20 feet unobstructed area in front of the rocket.
• Make sure that there is AT LEAST 10 feet unobstructed area behind the rocket for the fire ball...

• "Setup time is 45 minutes"

• Rocket is a one time shot. If it fails the jug will need to be cleaned and reset. I often setup two rockets in case of a failure.

Setup and Procedure:

1. Put the 4' aluminum track on the lecture demo cart as a ramp with the 4x4 block at one end propping it up.
2. Pour about 60 ml of ethanol into a beaker.
3. Make sure that the water jug is clean, dry, and does not smell bad. If it does, flush it out with either compressed air or water.

4. Make sure that the water jug does not have any cracks, that it isn't brittle or milky white. If so, throw it away, and get a new one.

5. Pour the ethanol into the water jug and swish it around A LOT.
6. Place the water jug up right with a stopper in the opening "loosely" so that the air and gas can leak out.
7. Let set for 10 to 20 minutes.
8. Move the cart into place, and carefully aim it in a safe direction.
9. Use either a match or lighter stick to ignite the rocket just outside the opening after you have the audience count down.

Cautions, Warnings, or Safety Concerns:

• Safety equipment is a must - glasses and hearing protection should be worn and a fire extinguisher should be present.
• Remember that when alcohol burns, the fire often can not be seen. Sometimes this can continue after the launch causing the plastic to burn. See photos below.
• Keep the rocket at least 8 feet from the wall or anything that can burn. The rocket produces a 5 foot flame that can be seen.

• DO NOT STAND BEHIND THE ROCKET....

Discussion:

When the ethanol vapor inside the jug ignites, it heats up very fast. This heat gives all of gaseous molecules a lot of kinetic energy. This causes the gas to expand. With nowhere else to go but out, the energetic gas flies out of the opening carrying with them a lot of momentum. Due to conservation of momentum, the jug must fly forward with some new velocity to make the net momentum zero. Thus, the more explosive the combustion, the farther our jug will fly.

References:

• The Physics of Rockets - Wikipedia

Demonstrations

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