List of Topics

SfC Home > Physics > Force > Friction >

 

Sliding Friction

by Ron Kurtus (revised 17 November 2016)

The most common type of friction encountered is sliding friction. This is the resistance to motion when you try to move or slide a solid object along the surface of another solid object.

When the external force pushing an object is not great enough to cause motion, the resistance is called static sliding friction. Once the objects are in motion with respect to each other, the resistance is called kinetic or dynamic sliding friction.

Interestingly enough, the static coefficient of sliding friction is greater than the kinetic coefficient, and thus more force is required to start to move an object than is needed to keep it moving.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Static sliding friction

When the external force pushing an object is not great enough to cause it to slide, the resistance is called static sliding friction. In other words, the object will not move when:

Fe < Fss

where

Static sliding friction equation

The equation for static sliding friction is:

Fss = μssN

where:

Transitional phase

When the external force equals the static sliding friction resistance (Fe = Fss), the object can break loose and start moving. The static friction becomes kinetic or dynamic sliding friction, which has a lower coefficient of friction.

This change from static to kinetic occurs rapidly but is not instantaneous.

Since the kinetic sliding friction is less than the static friction, the external force is greater than the kinetic friction.

Kinetic sliding friction

Once an object is sliding along a surface, the resistance is called kinetic or dynamic sliding friction.

Static sliding friction equation

The kinetic sliding friction equation is:

Fks = μksN

where:

Coefficients of friction different

The kinetic coefficent of sliding friction is less than the friction when the object is stationary or static.

μks < μss

This means that it is easier to slide a moving object than it is to get it to start moving.

Relationship to external force on sliding object

If an external force is acting on the object, it can accelerate, remain at a constant velocity, or slow down, according to the strength of the external force.

(See External Force and Sliding Kinetic Friction for more information.)

Acceleration

When the external force is greater than the kinetic sliding friction, the object will accelerate. This is the case when a stationary object breaks from the static to kinetic sliding mode.

Constant velocity

If the external force equals the kinetic sliding friction, the object will continue sliding at a constant velocity.

Slowing down and stopping

If the external force is less than the kinetic sliding friction, or has been reduced to zero, the object will slow down and ultimately stop moving.

Summary

Sliding an object along the surface of another object results in sliding friction. When the resistance to sliding is greater than the force pushing the object, it is called static friction. When the external force equals the static sliding friction, the object starts moving and transitions from the static to kinetic mode. Once the object is sliding, the resistance is call kinetic friction.

The external force acting on the object can cause it to accelerate, remain at a constant velocity, or slow down, according to the strength of the external force.


Help improve the lives of others


Resources and references

Ron Kurtus' Credentials

Websites

Friction Resources - Extensive list

Friction Concepts - HyperPhysics

Books

Top-rated books on Friction Science

Top-rated books on Friction Experiments


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


Share

Click on a button to bookmark or share this page through Twitter, Facebook, email, or other services:

 

Students and researchers

The Web address of this page is:
www.school-for-champions.com/science/
friction_sliding.htm
.

Please include it as a link on your website or as a reference in your report, document, or thesis.

Copyright © Restrictions


Where are you now?

School for Champions

Friction topics

Sliding Friction




Friction topics

Basics

Sliding friction

Rolling friction

Fluid friction



Let's make the world a better place

Be the best that you can be.

Use your knowledge and skills to help others succeed.

Don't be wasteful; protect our environment.

You CAN influence the world.





Live Your Life as a Champion:

Take care of your health

Seek knowledge and gain skills

Do excellent work

Be valuable to others

Have utmost character

Be a Champion!



The School for Champions helps you become the type of person who can be called a Champion.