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rotaional Inertia Feeler          

Presenter: Tony Wayne, Albemarle High School,        

Va. SOL:

PH.5  Newton’s Laws of Motion

National Standards:

Newtonian Mechanics


Rotational Inertia


·      “personal,” battery powered hand fan


Safety Considerations

            Tie back long hair so not to get it wrapped up in the spinning disk.


Hand these out to the students. Have them turn it on and rotate it around. Then ask them what they observe and what they can infer.

How the physics is demonstrated

The spinning disk increases the inertia or more specifically the rotational momentum. With rotational momentum the faster an object spins the more rotational momentum it has.

Construction  and Tips Regarding the Demonstration

This is home made using a “personal” fan. A personal fan is a small hand held fan powered by 2 “AA” batteries. The exact type does not seem to matter. The fan blades are removed. They can be torn off if the blades are made of foam. Glue a cd-rom onto the fan with epoxy. Kelvin electronics,,  ($25 minimum order) sells an adapter for small motors that allows a cd-rom to be converted to a wheel. This can be used with the fan it you pull the spinner off the motor’s shaft and put the adapter with the cd-rom attached in the motor’s shaft.

In place a cd-rom you can do the following:

Take apart a cassette player.

Under one of the spindles , there will be a large metal wheel. This wheel maintains the rotational speed of the spindle winding the cassette.

Pull the shaft out of this metal wheel.

The metal wheel can go on the fan’s motor’s shaft.

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