From Pep Rally to Chemistry Lesson: Ping Pong Balls and Liquid Nitrogen

Anything with liquid nitrogen tends to be both interesting and exciting. Couple it with an explosion, and you have a recipe for fun. I think that most science teachers would agree that associating chemistry with fun leads to an increase in student learning and engagement.

Several years ago, some of my former chemistry students approached me with a request to contribute to a pep rally. Tom Kuntzleman’s liquid nitrogen “bucket launch” came to mind. Doing this in the gymnasium seemed a little impractical because the buckets were advertised to go about 80-160 feet high! However, I had seen a few posts where people were sending numerous ping pong balls high into the air using what appeared to be the same technique. Either of these experiments requires a controlled explosion in a two-liter bottle. I read over Tom Kuntzleman’s Liquid Nitrogen, Gas Laws, and Rocket Science¹. All the information I needed was there, but I wanted to be certain that I was understanding everything correctly before attempting this experiment.

I spent the next week or so convincing myself that I should not bother Tom and that he was too busy to deal with my questions. False! When I finally emailed Tom, he responded quickly and invited me to call him so we could talk it over. I was both excited and surprised by this offer. Tom answered all my questions and encouraged me to write this article when I had executed the ping pong ball variation. That was approximately five years ago. I did write the article, but never submitted it because I just didn’t feel it was good enough. I attended ChemEd 2025 in Golden, CO, and spoke with Jon Holmes, who encouraged me to go ahead and submit the article. I was further motivated by Erica Posthuma’s presentation during the ChemEd X presentations.

I practiced with the bucket launch first to understand the timing. I learned to make sure the water was not too warm. With warmer water, the detonation would occur too quickly. Using room temperature water (or slightly cooler) provided at least 30 seconds. An awkwardly long delay may occur if the water is too cool or if the water level in the pot is insufficient.   

Once I was comfortable with the timing, I worked with our physics teacher to try the procedure. We practiced in an empty gym first. I’ve included a video of the explosion event and a slow-motion video version. The specifics of the procedure are described below.

Our science team has performed this explosion several times. Each time with great surprise and fanfare from the crowd. The explosion, the water vapor trail with a mass of colorful ping pong balls hurtling towards the gym ceiling, makes this a crowd-pleasing event. Every time I’ve done it, I always get questions in class about the science behind it, along with a lot of “what if we….?”. I encourage you to try this experiment and share in the fun.

Figure 1: Ping-pong balls launch into the air.

CITATIONS

1. Kuntzleman, T. Liquid Nitrogen, Gas Laws, and Rocket Science  ChemEdX  January 9^th, 2015 https://www.chemedx.org/blog/liquid-nitrogen-gas-laws-and-rocket-science

Procedure:

1. Load a trash bag with approximately 2000 ping pong balls.
2. Have an assistant nearby with the bag of ping pong balls.
3. Fill an 8-quart stock pot about one-third to halfway with tap water (18-23°C)
4. Center the can on the bottom of the can
5. Place an old beach towel (or other packing material) around the can to keep it in place and reduce the number of ping pong balls required to fill it.
6. Fill a dry 2-liter bottle about 1/3 full of liquid nitrogen. I pre-mark the bottles with a Sharpie™ ahead of time. Safety glass or face shield, ear protection, and gloves should be worn from this point until you are a safe distance from the ping pong-loaded can.
7. Tightly cap the bottle. It will not work if the cap is not tightly secured.
8. Working quickly with your assistant, load the ping pong balls into the trash can. You may want to practice this to make sure you are able to pour efficiently regarding pouring technique.
9. Step a safe distance away (at least 30 m) and wait for the fun!

• There will be some water spilled on the gym floor after, but it is easily cleaned up. I place a 10 x 10 tarp underneath to facilitate cleanup.
• Seventy to 100  ping pong balls are sacrificed each time. Sometimes, balls collide and form new ping pong combinations in the process. 
• Colored ping balls make this more visually appealing before, during, and after the explosion.
• Cleanup does take some time, depending on how many helpers are available. We average about 20 minutes for the cleanup.

SAFETY: If you plan to attempt this experiment yourself, I highly recommend starting the bucket launch. All the details required for safe and successful execution of the ping pong explosion HAVE NOT been fully described. If you try this experiment, you do so at your own risk. The 2-liter bottle should come from a highly carbonated soda rather than a non-carbonated drink. The pressure rating is much higher for the former. Be certain to tightly seal the bottle, use room temperature or below water, and keep yourself and any audience members at least 30 meters away from the detonation. If the bottle is not sealed properly, you may hear the characteristic hissing noises of a gas escaping. In the event the bottle is not sealed, DO NOT approach the assembly until you are certain all of the gas has escaped. This could take several minutes.

Materials Used

• Ping Pong balls purchased from Amazon in bulk
• Liquid nitrogen obtained from a welding supply shop
• Stockpot from Walmart
• Plastic trash can from Home Depot