Demos: 1F-04 Brass Rod (Inertia)

A long thin brass cylinder (rod) with flat ends is stood on its end on a sheet of paper. The rod balances very precariously, only a slight perturbance needed to topple it. But if the paper is pulled sufficiently rapidly, it will come out from under the rod without disturbing it.

Directions: Unlike the table cloth demo, even a quick yank here will likely topple the rod. The trick is to hold the paper end in one hand, then deliver a sharp blow with the side of the hand. This doesn’t always work on the first try, but persistence pays off.

Suggestions for Presentation: It is better if you do the table cloth demo first, then suggest how you might pull the paper out without toppling the rod. Students will likely suggest a quick yank. Show that this doesn’t work.

A companion demo to this is to place two glass pop bottles (harder to find these days!) mouth to mouth in a vertical orientation with a dollar bill wedged between them. Tell the students that you will give the dollar bill to anyone who can get it out without toppling the bottles (or touching them). The trick is to hold the bill like the paper in the brass rod demo and give it a sharp blow with your hand or with your index finger.

Applications: Relate this to the other inertia demos.

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