A paintball hits a cardboard target, played back at 1/67 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 differently a shot from 15 feet and a shot from 30 feet might arrive at the target. (Since this was just an exercise to gather background information, she generously granted me permission to share it.)

Her husband took shots at a target next to my lab’s high-speed camera. We recorded shots from several distances, and I analyzed the videos to measure the paintball’s incoming velocity.

In most cases, the paintball completely 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, meaning 0.0005 or 0.001 seconds. 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.

With a trip to the toy store and an hour of snapping and unsnapping LEGOs, I came up with a little gearbox connecting a motor to a stirring rod. The gears give this light-weight motor the mechanical advantage that it needs to churn thickening ice cream. For each turn of the rod, the motor spins 15 times.

The assembly — shown with some spare pieces attached as stirring implements — fits snugly into a large empty yogurt container with notches cut in the sides.

Ice cream is milk : cream : sugar in the proportion 2 : 2 : 1 with a pinch of salt and flavoring. Just mix them and agitate the mixture while it freezes. (Other, more complicated recipes involve heating the milk and using eggs too. No need for more complication here.)

I let it chill in peace for about an hour. At 7:30, when I could see ice crystals starting to form, I switched on the motor, headed out the door for the evening, and hoped for the best. Around midnight, I came home to a delicious success!

Thanks to Jeff Potter for sharing the idea of LEGO ice cream makers in his book. With the help of the enthusiastic people at Shananigans Toy Shop, I decided on LEGO Power Functions (#8293) for a motor and LEGO Crazy Action Contraptions (Klutz Press) for a starter set of bricks. It was just the right number of pieces to give me room to experiment and create something sturdy enough. Try making one yourself!

A guys’ singing group I formed with some friends in high school has been carried on by some younger guys and a sort of spin-off girls’ group. I arranged this for them based on my memory of a live performance we saw about five years ago. It’s nothing fancy, but it made a strong impression.

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1. Make a fist around two fingers and squeeze hard for half a minute or more. Then relax your fist, but don’t open it. Delicately slip the fingers out, and then gently try to open your fist.
2. Stand in a doorway. Push your arms outward, pressing the backs of your hands hard into the doorframe. Do this for at least half a minute. Step out of the door and let your arms and shoulders relax.
3. Lie on the floor on your back. With your legs straight (knees locked) have a friend pick up one leg and lift it up until it is stretched a little farther than what’s comfortable. Hold this way for half a minute. Finally, close your eyes while your friend lowers your foot slowly back to the ground, holding it by the toe.

The first one in particular is good for moments when you are waiting around or standing in line with a friend. If you know more of these, post them in the comments.

This is my low-fi sketch of Jason Robert Brown’s ”Bad, Bad News” from 13, arranged for my buddies in OBOC. (This was performed in a revue with free admission. And it is certainly not thorough enough to replace an authentic arrangement. But if you wish I would take it down, a polite email will suffice.)

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I wrote a Beats-per-Minute calculator. Tap any key to a beat and it will display the tempo. It’s a step more refined than other similar tools because it shows correct precision and it changes color once it has an accurate reading. Try it!

This is a screenshort. Click it open the BPM calculator.