Triumph of the BelmSled

Di and I donated tickets to the Boston Museum of Science to Miles’s fourth grade class. His teacher, Ms. Mullen, asked if we would would like to attend, knowing our mutual interests in science would help her in answering questions raised by the kids.

One of the scheduled activities was a visit to the Design Challenge area, where kids could learn about a basic physical principle and then build something that worked with that concept. This month’s concept was friction; the design challenge was to build either the fastest or slowest “sled” to race down a series of teflon tracks. After noticing the task’s similarity to the Pinewood Derbys of my Cub Scout youth (and choking back the horrible failure flashbacks), I set to work.

We were each given a plastic tray to which we could attach our design modifications. There were different fabrics that could be used to cover the tray bottoms, weights that could be added, pipe cleaners, straws, and large and small binder clips. We could run each trial design on the tracks, which were equipped with LED sensors and timers accurate to a hundredth of a second.

Even though I didn’t major in an engineering discipline, the pressure was on — the MIT guy had to make a good showing in front of a bunch of 9-year-olds. First I tested the unadorned tray on the track: it took 1.5 seconds to travel to the bottom. Thinking that a pair of runners would produce the least amount of friction, I clipped two of the straws across the tray bottom using the small binder clips. (I had already figured out that two small clips weighed less than one large clip.) Here’s what I came up with:

The BelmSled

Very simple. The runners are spaced far apart for stability and pulled tightly against the tray bottom to prevent bouncing.

My first test run on the track set the new record for the day:


Miles and his classmates noticed my win and started asking me questions about what I did. I looked at each of their sleds, asking how each might be made faster, letting them come up with the answers. It only took two minutes before one of them set a new record.

Everyone had fun, Miles’s class learned few things, and I had a “teachable moment.” What more could I ask? Oh, maybe fewer fart jokes during lunch.

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