Coefficients of Kinetic and Static Friction

14.04.2017
Friction Coefficient

What is friction?

Friction is a force resisting relative motion and it occurs at the interface between the bodies, but also within the bodies, like in case of fluids. The concept of friction coefficient was first formulated by Leonardo da Vinci and is defined according to the following equation:

*** QuickLaTeX cannot compile formula:

\begin{eqnarray*}
\mu = F_f/F_N
\end{eqnarray*} 

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

where

*** QuickLaTeX cannot compile formula:
F_f

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

is the friction force and

*** QuickLaTeX cannot compile formula:
F_N

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

is the applied normal load. The magnitude of the coefficient of friction is determined by the properties of the surfaces, surroundings, surface features, presence of the lubricant, etc. A list of typical friction coefficients can be found here.

banner

Static vs Kinetic Friction

Typically friction can be distinguished into static friction and kinetic friction. Static friction force 

*** QuickLaTeX cannot compile formula:
F_{fs}

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

is the friction force prior the initiation of motion. Kinetic friction (also known as dynamic, or sliding) force 

*** QuickLaTeX cannot compile formula:
F_{fk}

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

is the friction force developed during the motion. It should be noted that these forces are different with a following relation holding in most situations:

*** QuickLaTeX cannot compile formula:

\begin{eqnarray*}
F_{fk}<=F_{fs}
\end{eqnarray*} 

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

Correspondingly, there are two friction coefficients, static  

*** QuickLaTeX cannot compile formula:
\mu _s

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

and kinetic friction  

banner
*** QuickLaTeX cannot compile formula:
\mu _k

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

coefficients.

Static friction coefficient is calculated according to the following equation:

*** QuickLaTeX cannot compile formula:

\begin{eqnarray*}
\mu _s = F_{fs}/F_N
\end{eqnarray*} 

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

Kinetic friction coefficient is calculated according to following equation:

*** QuickLaTeX cannot compile formula:

\begin{eqnarray*}
\mu _k = F_{fk}/F_N
\end{eqnarray*} 

*** Error message:
Cannot connect to QuickLaTeX server: cURL error 7: Failed connect to www.quicklatex.com:443; Connection timed out
Please make sure your server/PHP settings allow HTTP requests to external resources ("allow_url_fopen", etc.)
These links might help in finding solution:
http://wordpress.org/extend/plugins/core-control/
http://wordpress.org/support/topic/an-unexpected-http-error-occurred-during-the-api-request-on-wordpress-3?replies=37

See this introduction video regarding the static and kinetic friction forces:

I am currently working as a Postgraduate Researcher at the University of Leeds, where I am actively involved in research activities. Prior to this, I successfully completed my master's degree through the renowned Erasmus Mundus joint program, specializing in Tribology and Bachelor's degree in Mechanical Engineering from VTU in Belgaum, India. Further I handle the social media pages for Tribonet and I have my youtube channel Tribo Geek.

Be the first to comment

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.