Mechanics:
Interleaved Phone Books

PIRA Class: 1K20.25

Purpose:
Demonstrate how traction can lead to an increased friction force.

Description:

Two pads of Post-It notes, 50 pages each, have been interleaved. A student can pull on each end of the pad with great force without separating the pages.

The increased thickness in the interleaved region causes each page to form an angle theta. Your horizontal pull on the ends of the pads results in an angled tension exerted through each page. The vertical component of this tension increases the normal force between neighboring pages thus the harder you pull, the higher the normal force and the higher the resulting friction force keeping the pads together.

Equipment:
Two interleaved Post-It pads (already setup in the container)

Location:
Shelf 123

Extras:
Mythbusters on interleaved phone books
Discussion of this demo setup
Physics Today article with more details
A demo to setup for the future