#modphys 24/180: A €2 Dynamics Track

We have been working on the Constant Acceleration Particle Model over the past week. I introduced the topic using video analysis with LoggerPro, but unfortunately we haven’t been able to get convincing v/t graphs. I suspect a combination of clumsy fingers, air resistance, careless clicking, and LoggerPro’s obnoxious approach to derivatives (second order Newton-Raphson?). Combined with the need to prepare for a practical, it was time to go tangible for the deployment lab.

I really wish I had a proper dynamics system, but unfortunately the money just isn’t there. I spent a lot of time rolling carts, cylinders, and balls down ramps before I discovered that the Vernier motion detector works just fine inside a pipe.


For some reason (perhaps a type of resonnance?) the face of the motion detector needs to be slightly off-center. But I was able to detect a marble within the pipe above to about the length of the 3 m pipe. The graphs from this motion are below. The a/t graph is pretty noisy, but I think I could convince myself of a constant value. The v/t graph is clear enough to show the effect of rolling friction.

I also tried one of my plastic cars in a larger pipe (formerly used for a perfume diffusion experiment, so it retains an aura of synthetic mystique). It seems to work well. The wheels roll only on their outer rims, which should help to reduce frictional effects and keep the car moving straight.



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