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Resistive Force of Friction

Uses of Friction

Causes of Friction

Standard Friction Equation

Changing Sliding Friction on Hard Surfaces

Coefficient of Friction Values for Clean Surfaces

Coefficient of Friction Values for Greased Surfaces

Role of Friction in Starting Rolling Motion

Rolling Friction

Rolling Friction and Automobile Tires

Traction Friction of Tires

Decreasing or Increasing Fluid Friction

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Listing of the coefficient of sliding friction values for a variety of hard greased materials - Succeed in Understanding Physics. Also refer to Physical Science, static, kinetic, surface roughness, clean, lubricated, scientific measurements, engineering tables, scientific method, Ron Kurtus, School for Champions. Copyright © Restrictions

Coefficient of Friction Values for Greased Surfaces

by Ron Kurtus (2 November 2005)

Engineering laboratories have measured the coefficient of friction for a number of materials that are lubricated by grease and have tabulated the results. These coefficient of friction values apply only to sliding hard surfaces against each other. Since various experimental parameters such as the type of grease are not listed, considerations should be made in using these tabulated values because they may not directly relate to your application.

Questions you may have include:

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Note: Click the Play button to hear the text being read.

Time = 3 min. 30 sec.

Useful tools: Metric-English Conversion | Scientific Calculator.

Considerations

The information available on the various coefficients of friction provide a starting point on the subject, but unfortunately the values lack a good scientific basis.

Condition of materials

Effective scientific measurements typically state the exact condition of materials and that of the surrounding environment. Although lubrication with grease may negate the surface roughness factor of the materials, it is still good scientific practice to document the roughness. Another needed factor is the physical condition of the materials.

Test setup

Describing the test setup is important in order to allow others to duplicate and verify the measurements. With friction, the normal force can be a factor in the case of hard materials that may deform slightly under high pressure. That value should be part of the test description.

Testing environment

It is also important to state the testing environment. Although it is unlikely measurements were made under extreme temperature and humidity conditions that affect the coefficient, at the very least those items should be noted.

Greased materials

The static and kinetic coefficients of friction were measured for a variety of materials where "grease" was used as a lubricant. A major problem in using these readings is that we do not know what type of grease was used. Lubrication can vary considerably, depending on the material.

Another factor is the thickness of the lubricating lever of grease. It is assumed a thin coat of grease it used. A real thick coat of grease could greatly change the coefficient values.

Table

The values in the following table show that measurements on most materials seemed to be either static or kinetic. The reference source of the values listed does not indicate why both types of friction were not measured.

You can use these values for the coefficient as a guide, but it is best to perform some tests and measurements in your specific application to get good values.

Coefficient of Sliding Friction (greased surfaces)

Material 1

Material 2

Static

Kinetic

Aluminum Aluminum 0.3 -
Bronze Steel 0.16 -
Cadmium Cadmium 0.05 -
Cast Iron Cast Iron - 0.07
Cast Iron Oak - 0.08
Chromium Chromium 0.03 -
Copper Copper 0.08 -
Copper Mild Steel - 0.18
Diamond Diamond 0.05 - 0.1 -
Diamond Metal 0.1 -
Glass Glass 0.1 - 0.6 0.09 - 0.12
Glass Metal 0.2 - 0.3 -
Graphite Graphite 0.1 -
Graphite Steel 0.1 -
Hard Carbon Hard Carbon 0.12 - 0.14 -
Hard Carbon Steel 0.11 - 0.14 -
Iron Iron 0.15 - 0.2 -
Leather Metal (clean) 0.2 -
Magnesium Magnesium 0.8 -
Nickel Nickel 0.28 0.12
Nickel Mild Steel - 0.18
Oak Oak (cross grain) - 0.07
Platinum Platinum 0.25 -
Plexiglas Plexiglas 0.8 -
Plexiglas Steel 0.4 - 0.5 -
Polystyrene Polystyrene 0.5 -
Polystyrene Steel 0.3 - 0.35 -
Polythene Steel 0.2 -
Sapphire Sapphire 0.2 -
Silver Silver 0.55 -
Sintered Bronze Steel 0.13 -
Steel Brass 0.19 -
Steel (mild) Cast Iron 0.18 0.13
Steel Cast Iron 0.12 -
Steel Copper Lead Alloy 0.16 0.15
Steel (hard) Graphite 0.09 -
Steel Graphite 0.1 -
Steel (mild) Lead 0.5 0.3
Steel (mild) Phos. Bros - 0.17
Steel (hard) Polythene 0.2 -
Steel (hard) Polystyrene 0.3 - 0.35 -
Steel (mild) Steel (mild) - 0.09 - 0.19
Steel (hard) Steel (hard) 0.05 - 0.11 0.03 - 0.12
Teflon Steel 0.04 0.04
Teflon Teflon 0.04 0.04
Tungsten Carbide Tungsten Carbide 0.12 -
Tungsten Carbide Steel 0.08 - 0.2 -
Zinc Zinc 0.04 -

Summary

Coefficient of friction have been measured for a number of hard, greased materials. A problem occurs with the values in the table concerning the type of grease used. Considerations should be made in using this tabulated material, since it may not directly relate to your application.

Answers to Readers' Questions


Be excellent in your work


Resources

The following resources provide information on this subject:

Websites

Engineer's Handbook - Coefficient of Friction

RoyMech (UK) - Friction Factors

Physics Resources

Books

The following books are available from Amazon.com.

Basic

Complete Idiot's Guide To Physics by Johnnie T. Dennis; Alpha (2003) $18.95

What Is Friction? (Ages 4-8) by Lisa Trumbauer; Children's Press (CT) (2004) $4.95

Advanced

Friction and Lubrication in Mechanical Design (Mechanical Engineering Series) by Ali Seireg; Marcel Dekker Pub. (1998) $199.95

Physics of Sliding Friction (NATO Science Series E:) by B.N. Persson, E. Tosatti; Springer Pub. (1996) $358.00


Mini-quiz to check your understanding

1. Why should environmental conditions be mentioned?

Because the environment is important to everyone

Grease gets thicker in colder temperatures, affecting the coefficient

Grease gets thicker in a humid climate, affecting the coefficient

2. Should the type and amount of grease be stated in listing coefficient?

No, because only surface roughness determines friction

No one is sure whether the type makes any difference

Yes, because lubrication varies greatly with material

3. When should you make your own friction measurements?

When the exact amount of friction needs to be known

When the normal force varies

You do not need to use anything but a table of values

If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.


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