I have listed a few of my favorite YouTube channels in previous posts, but I neglected to mention Numberphile. Numberphile posted a new video a few days ago, where Matt Parker showed how linked circles can roll. He demonstrates how it works and how far the circles must overlap. They must be overlapped the correct amount so that the center of mass of the two circles does not move up and down. The video goes through the proof that this is the correct way to link the circles, but it made me think, “What if we overlapped the circles too much or too little?”
So I took some old CD’s and cut the slots 1.76 cm (ummm… well it was somewhere close to that). We tried it out by rolling it on the floor and it worked well, but it was kind of hard to figure out how to push this strange shape. So we rolled it down a very slight incline.
Then I cut smaller slots in another pair of CD’s. They clearly did not roll as well. (Sorry for the sideways video)
Then we tried larger slots. Once again, it did not roll as well.
Isaiah wanted to race the good one and the one that had small grooves.
Taking someone else’s idea and creating variations is a great way to invent your own science experiments. Next time you see a science activity, try to think of some variations (or have your kids think of them) and turn it into a real experiment.
If you get a chance to make these, it is very fun and interesting to watch them roll. I wonder if there is or ever will be a useful application of this idea?