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Why Do Ping Pong Balls Burn?

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Ping pong balls are made from a flammable plastic.

Ping pong balls are made from a flammable plastic.

Anne Helmenstine

Question: Why Do Ping Pong Balls Burn?

Old ping pong or table tennis balls would sometimes combust or explode when hit, which made for an exciting game! Modern balls are less sensitive, but if you take a lighter to a ping pong ball, it will burst into flame, burning like a tiny flamethrower. Do you know why ping pong balls burn? Here's the answer.

Answer: Some people think ping pong balls must be filled with some flammable gas, but they only contain regular air. The secret to the spectacular way they burn is in the composition of the actual ball. Ping pong balls burn because they are composed of celluloid, which is like gun cotton or nitrocellulose. It's extremely flammable. The old balls consisted of acidified celluloid, which became increasingly unstable over time. The slightest spark or heat from friction could ignite these balls.

How To Ignite a Ping Pong Ball

You can try this project yourself. All you need is:
  • ping pong ball
  • long handled lighter
  • fire-safe surface
If you look around online, you'll see people lighting ping pong balls while holding them. Usually what they are doing is lighting the ball from the top. No matter where you light it, most of the heat escapes above the ball, but they burn so rapidly, it's a bad idea to try to hold one. You'll almost certainly burn yourself, plus you could catch your clothes or hair on fire. Also, there is a chance the ball could explode, which would spread the flame and may result in injury.

A better way to light a ping pong ball is to set it on a fire safe surface (e.g., metal bowl, brick) and light it with a long-handled lighter. The flame shoots up fairly high, so don't lean over it and do keep it away from anything flammable. It's best to do this outdoors, unless you want your smoke alarm to go off.

A variation of the project is to cut a hole in a ping pong ball and light it from the inside with a match. The ball will disintegrate while you watch.

How Ping Pong Balls Are Made

A regulation ping pong ball is a 40 mm diameter ball with a mass of 2.7 grams and a coefficient of restitution of 0.89 to 0.92. The ball is filled with air and has a matte finish. The material of a regular ball isn't specified, but balls typically are made from celluloid or another plastic. The celluloid is a composition of nitrocellulose and camphor that is produced in a sheet and soaked in a hot alcohol solution until it is soft. The sheet is pressed into hemisphere molds, trimmed, and allowed to harden. Two hemispheres are glued together using an alcohol-based adhesive and the balls are machine-agitated to smooth the seams. Balls are graded according to how evenly weighted they are and how smooth they are. Part of the reason people may think the balls are filled with a gas other than air is because the plastic and adhesive off-gas into the interior of the ping pong ball, leaving it with a chemical odor, similar to that of photographic film or modeling glue. Based on the likely composition of the residue, reports that inhaling the gas inside a ping pong ball produces a "high" may be justified, but the vapors almost certainly are toxic, even though the ping pong ball itself is not. While there is no rule that the balls be filled with air, it's the simplest means of manufacturing them and there hasn't been a reason to form the balls filled with other gases.

Watch a video of this project.

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