# Homework Help: Measuring coefficient of friction with only a ruler

1. Oct 27, 2004

### freemind

Hello,

I'm stumped about a relatively simple problem. Here it is in its exact form:

"You need a rectangular prism with its height at least several times greater than its length. Put this prism vertically on a table or any other horizontal plane. How does one determine the coefficient of friction between the prism and the plane using only a ruler as a measurement equipment? You can use any facilities for the goals other than measurements."

Now, two things. First, it is not stated which coefficient to find (static or kinetic) and secondly, i don't know what to make of the last statement. How does one measure the coefficient of friction w/out "making any measurements". (I'm ignoring that sentence for now)
Anyway, my idea is to position the prism at a certain point and lift the table, measure the height at one end and see how far it slides. Yet, i have the feeling that it would be smarter to use the refractive properties of the prism itself to measure the coefficient. I have no clue how to do that.

Please try to destroy or append to my ideas.

Thanks

2. Oct 28, 2004

### Tide

Tilt the table! Measure the distance from the top of the prism to the point directly beneath it on the surface of the table and the distance between . This, along with the length of the prism, allows you to calculate the angle at which the table is tilted. The angle at which the prism slides allows you to calculate the coefficient of friction.

3. Oct 28, 2004

### freemind

Thank you very much Tide. That was too easy!