# Sliding Friction - Lecture Table And Felt

## Purpose

To show the effect on frictional force of (a) velocity, (b) normal force, and (c) contact area.

## Equipment

Two aluminum blocks, one having felt on two sides, spring scale with handle, rope, cleaning rag.◙

## Suggestions

Practice may be necessary. Clean the surface so that the frictional force is not reduced by lots of dust.◙

## Description

The spring scale is connected by the rope to the friction block, which has one of its felt-covered sides◙contacting the table. Pull with the rope parallel to the table so that the spring scale is visible to the class. Several features of frictional force are demonstrated as follows: (1) Static versus sliding friction, by slowly increasing the pulling force until the block begins to move. The force required to keep the block moving at a constant slow velocity is less than the force required to break the static friction and start the block in motion. (2) The frictional force doubles when a secon

(PIRA 1K20.00)◙