Experimentally determining moment of inertia using a simple pendulum

If you want to do a fun experiment that involves the parallel axis theorem and pendulum dynamics… try this for your vex wheels.

I took a shot at the 5 in wheel and came up with I_wheel = 0.00051 kg m^2 which is an equivalent radius of 2.1 inches if the mass is on the rim only. I would like others to try their wheels.

Of course if you have a nice instrumentation system, you could measure the wheel acceleration with a known torque to get the moment of inertia. e.g. Logger pro sensors in a physics class, but all I needed was a stop watch and a scale.

This is a great experiment. Except for spinning kids around in an office chair (sorry about that, guys), it’s hard to come up with DIY experiments that demonstrate how moment of inertia is dependent on mass distribution. Vamfun’s idea actually gives you some numbers to work with if you really want to understand the physics of this game. And I think this year’s game requires kids to really think about what’s going on with mass and energy and aerodynamics. It’s not going to be so easy to simply copy somebody else’s design by looking at it: much of the robot’s performance will be the result of these kinds of concepts embedded in software and such.

Thanks for posting this!