What is friction?

The Most Common Origin of Friction

Friction exists because most surfaces really look like this under a microscope.

Note the hills, the crests and the valleys. These are called asperities, or material deformations. They occur on rough surfaces, and even flat surfaces might have minor irregularities on it.

Now imagine trying to rub them against each other. Feel, for a moment, in your mind’s eye the opposition you are likely to encounter as they grind against each other.

That grinding is the most common origin for friction, both static (when your object is still and you’re trying to get it to move) and kinetic (when your object is already moving, and you need to keep it moving).

It is why the friction that wheels encounter while rolling (called rolling friction) is much lower than other types of friction, and why tyres have deep grooves in them. It is also why friction tends to decrease the flatter and more uniform your surface gets.

Friction for Flat Surfaces

But friction can still exist for perfectly flat surfaces, where asperities of the form above are no longer present.

Perfectly flat surfaces bond to each other - in other words, they try to stick to each other. This is called adhesion, and can be caused by any number of reasons:

  • van der Waals forces, a class of forces where attraction between electric dipoles on the surface of the material cause them to be attracted. In such cases, the materials are said have been dispersively adhered.
  • chemical bonding, where the atoms of the two materials exchange electrons in some way and become chemiially attached to each. For instance, hydrogen in one material may form tenuous bounds with strongly electronegative elements in the other.

These forces are typically weak enough that they are easily broken once you lift the object - but not so weak that overcoming the attraction by dragging the object doesn’t pose a problem.

Finally, a Definition

Friction, then, is not so much a force as it is the sum of very tiny forces and irregularities along the edge of surfaces.

It is possible to model it as a true force - and indeed, most high school textbooks do just that - but it is important to recognise that that is just a convenient abstraction. Friction is to forces what Santa Claus is to a jolly man in a fat suit: window dressing on top of a very complex reality.

This information was taken from Quora. Click here to view the original post.

Do you have something to add or discuss? You are welcome to do so in the comments below! And remember to share it with your friends!

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What are your thoughts on this subject?
Darlene Davidson
This is a very complex question and answer. I think it is a convenient abstraction.
Mar 16, 2021 5:34PM
Robert Mookerdum
Always use lubes.
Feb 12, 2020 4:50AM
Ilias Tsiabardas
Good information on friction
Nov 5, 2019 6:15PM
Thanks for nothing.
Aug 6, 2019 5:37PM
Robert L Hutchison
It would seem the world would not work like it does without friction!
May 13, 2019 5:07PM
Dave Fritsch
Facinating. Makes me want to go back and retake physics.
Apr 2, 2019 2:14PM
Alicia Pettigrew
thanks. this was a real physics class. i get the friction.
Jul 20, 2018 5:38PM
Christopher Collins
Very good
Jul 15, 2018 8:11AM

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