A paintball hits a cardboard target, played back at 167 of its actual speed.

Katherine Nash Scafide, who is studying nursing with a specialty in forensics, recruited me to help her measure the impact force of a paintball. Her work focuses on the bruising, but for my part we didn’t use any human targets. We wanted to know how much firing distance mattered — how much worse is a shot from 15 feet than a shot from 30?Her husband took aim next to the Leheny lab’s high-speed camera. I analyzed the videos to measure the paintball’s incoming velocity.

paintball velocity vs. distance

Usually, the paintball smashed onto the target without backward splashing or flying bits. (The video above was an exception, a neat-looking one.) The impact occurred during one or two frames of high-speed video, about a thousandth of a second. From this and the paintball’s mass (3.2 grams) we can get an estimate of impact force. Fired at 15 feet, the average force during impact is in the range of 250-500 Newtons, or 45-90 pounds. Ouch.

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