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# Friction Experiment: Measure Coefficient of Friction with a Scale

by Ron Kurtus (revised 16 November 2012)

Friction is a resistive force caused when two objects are in contact with each other. There are some simple experiments to determine the force of friction and the coefficient of friction.

The coefficient of friction is a number that determines how much force is required to move an object that is held back by friction.

Questions you may have include:

- What is the purpose of the experiment?
- What research must be done?
- What is the experiment?

This lesson will answer those questions.

## Purpose of experiment

The purpose of this experiment is to demonstrate how you can measure the coefficient of friction with a scale.

## Background

The equation for this is:

F_{r}= f_{r}x N

where

**F**is the resistive force of friction or the amount of force required to overcome friction_{r}**f**is the coefficient of friction between the two surfaces_{r}**N**is the normal or perpendicular force pushing the two surfaces together

If the force pushing to surfaces together is gravity, then **N** equals the weight of the upper object.

### Static and kinetic

For a sliding object, the static coefficient of friction results in the force required to start the object moving. Once the object is sliding at a steady rate, the kinetic coefficient of friction results in the force required to keep the object moving at that velocity.

### Two surfaces

Note that you must record what the two surfaces are. The coefficient of friction is always for two surfaces. For example, you could find the friction between wood and steel, wood on wood, rubber on wet pavement, and so on.

## Method

One way to determine the coefficient of friction between two surfaces is to pull on an object, using a spring scale that is used to measure weight. If you lay an object on another surface and then pull it, you can determine the amount of force required to move the object.

The coefficient is then

f_{r}= F_{r}/ W

where ** W** is the weight of the upper object.

First you pull slowly until the object just starts to move. Record the force and calculate the static coefficient of friction.

Then drag the object along at a steady velocity. Record the force on the scale and calculate the kinetic coefficient of friction.

## Summary

By using a scale, you can measure the coefficient of friction.

Think of different ways to do things

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friction_measure_coefficient_with_scale.htm**

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## Where are you now?

## Measure Coefficient of Friction with a Scale