This is one of my favorite science toys! I keep a mini ping pong ball cannon in my class at all times because it is a fun way to get the students attention. And, at every STEM Magic Show I start with the ping pong ball cannon to kick things off with a bang! The cannon is quite easy to build and is a great tool for teaching concepts in science.
How to build a a Ping-Pong Mini-Cannon
Supplies (all links re-direct to Amazon.com)
Building the Cannon (watch the video for details)
Remove the plastic nozzle from the battery filler. Save the rubber 'bulb'.
Make a hole in the rubber bulb about half way between the end and the opening using an awl, scissors or nail.
Disassemble the lantern lighter and remove the angled bracket.
Insert the lantern lighter into the rubber bulb so that the flint and steel are inside the bulb and the handle is outside the bulb.
Re-assemble the lantern lighter.
Add a few drops of methanol** and place a ping pong ball into the opening of the rubber bulb **Read Warnings and Safety Precautions before attempting**
Turn the handle on the lantern lighter and the ball will shoot out.
**Warnings and Safety Precautions**
This demonstration should only be performed by people who have had proper training.
-Methanol is very flammable and is very dangerous. Methanol vapors ignite very easily and, because methanol vapors are heavier than they air around them, they will 'flow' like an invisible liquid and will catch fire if exposed to heat or open flame.
-The projectile can be very dangerous, do not point at other people or at yourself.
-The flame will continue to burn inside the bulb after you'd launched the ping pong ball. Be sure to blow it out and DO NOT add more methanol when the inside of the bulb is on fire or is still hot.
The Science of the Ping Pong Mini-Cannon
Methanol is highly flammable and combusts in the presence of oxygen (see chemical equations below). As the methanol burns, the heat from the reaction takes up more space - hot air expands because of increased energy, think of a hot air balloon. This rapid expansion of the air inside the bulb causes the pressure to increase very quickly and the ball is ejected from the cannon.
Equations for the Combustion Reaction of Methanol:
Word equation: Methanol and Oxygen react to form Carbon Dioxide and Water
Chemical Equation: CH3OH + O2 -> 4H2O + CO2
Balanced Chemical Equation: 2CH3OH + 4O2 -> 4H2O + 2CO2
Keep on Learning!