Title: Flaming Rocket Jug demo
[WARNING: extreme caution should be used for this demo as it involves ethanol gas, flames, and projectiles. DO NOT try this at home or in any crowded space]
Demo overview:
This demonstration involves igniting flammable vapor that has built up inside a large water jug that has been placed on an elevated metal rail, resulting in the jug being launched off of the track. While this demo can be used to cover physics topics such as thrust and Newton’s 3rd law of motion, I conducted the demo in the context of explaining Earth’s gravitational acceleration. When rockets are launched, they must “beat” Earth’s gravity to leave the atmosphere.
Presenter Notes:
Demo Explanation (towards a general audience):
Preamble
Earth’s gravitational acceleration, given as 9.8 m/s^2, is the reason why we’re on the ground. Without it, a single jump could send you flying off into outer space. This number characterizes the rate at which objects fall back to Earth. If I go skydiving and jump out of a plane, for each second that passes, my speed toward the ground will increase by 9.8 m/s, or roughly 32 ft/s! That’s pretty fast! To demonstrate the strength of gravity, I’ll try to beat it with my very own rocket launch. Anytime we launch a rocket into space, it must be going fast enough to beat Earth’s gravitational influence.
Demo
This jug will be my rocket. It has a highly flammable gas inside of it, and I’ll be lighting it with electric sparks from this small tesla coil. Once the gas has ignited, the flames that shoot out of the bottle will generate thrust causing it to launch forward. (Be sure to warn people near the demo of flames and heat from the back of the jug and request someone to have a fire extinguisher handy just in case)
Post-Demo
Well, the rocket launch wasn’t as successful as I had hoped, but this demonstrates the raw power of Earth’s gravity. Even though my rocket produced a lot of thrust, Earth’s gravity brought it right back down to the ground!
Demo Instructions:
Before the show
- Pour 60 mL of 100% ethanol into the water jug before the start of the show
- Be sure to swirl the ethanol around to coat as much of the inner surface area of the jug as possible
- Fix a metal clip onto the mouth of the jug
- This will provide a solid conductor for the tesla coil arc to produce ignition
- Loosely place a cork in the mouth of the jug
- We want the ethanol vapors being produced to push air out of the jug
- Place the jug on the cart for the duration of the show until the demo is due to begin
- Ideally, we’d want at least 20-30 mins for the ethanol vapors to build
- Ensure the metal rail is elevated to a reasonable angle using a block or wedge
- Ensure that the hand-held tesla coil is plugged in and will be ready for use later
- Have a fire extinguisher and a fire-resistant glove nearby
During the show/demo
- Swirl the ethanol around the inside of the jug once again
- Make sure that the ethanol coats the inside of the neck of the water jug…this is important to properly ignite the fumes
- Empty a good portion of the excess ethanol into a nearby sink
- This is done to avoid the potential spilling of flaming ethanol during launch and to mitigate the possibility of the jug still being on fire when it lands
- You will likely get ethanol on your hand during this part
- Remove the cork from the jug and place it on the metal rail
- Make sure that the cart is positioned sufficiently far from flammable objects as the flames that shoot out of the back of the jug can reach a few feet
- Make sure that the cart is angled appropriately to avoid launching the jug at someone
- Have someone nearby grab the fire extinguisher
- Have another person grab a fire-resistant glove and head to the opposite end of the room
- Turn the knob near the tesla coil handle far to right to activate the tesla coil
- Begin a countdown…I mean come on, you have to for a rocket launch
- When you’re ready, bring the coil near the metal clip on the mouth of the jug for the tesla coil to arc to
- Once launched, check to see if any flaming liquid has spilled out of the jug and act accordingly
- Once the bottle lands, have the person with the glove grab the jug, placing the glove over the mouth of the jug to extinguish any potential fire if the ethanol is still burning
- Place the jug back on the cart
Aftermath
- Dump any remaining spent ethanol into the sink
- Use a compressed air nozzle to force out the toxic fumes left inside the bottle
- This is important as these fumes may affect future launches if not properly vented out of the jug
Main Safety Concerns:
- Potential for flaming excess ethanol to be ejected out of the bottle during the launch
- Potential to ignite curtains or other nearby flammable objects too close to the mouth of the bottle during launch
- Potential to possibly ignite yourself on fire
- If you get ethanol on your hand during the dumping of excess ethanol, be extra careful when you go to ignite the fumes inside the jug
- Potential for jug to land near people or to go into the audience
- Be cautious of how the cart is angled when launching
- Potential for jug to still be on fire when it lands…it will begin to melt if this is the case
- Ethanol fires may be hard to detect by eye alone!