How Do Attractive and Repulsive Electromagnetic Forces Combine in Contact Force?

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
7 replies · 2K views
rahaverhma
Messages
73
Reaction score
1
If friction is electromagnetically attractive force and the normal reaction is electromagnetically repulsive force which it obviously is. But how is it possible to have different type of force as the component of a single force i. e. Contact force over the nature of which I have got confused!
 
Physics news on Phys.org
phinds said:
I think you're getting lost in the weeds. They are all mechanical forces of things pushing on things.
But it's origin is electromagnetic. And friction does not push.
 
rahaverhma said:
But it's origin is electromagnetic. And friction does not push.
If you have a bridge constructed of trusses, all members are in compression or in tension. No shear forces anywhere. Yet the bridge as a whole resists shear. Sometimes the whole is different than the parts.
 
rahaverhma said:
And friction does not push.
Yes, it does. It's two rough surfaces sliding over each other with small areas of each sticking into gaps in the other and the surface electrons repel each other. Think of two sawtooth waves "sliding" over each other.
 
  • Like
Likes   Reactions: Dale
rahaverhma said:
But it's origin is electromagnetic. And friction does not push.
Yes, it does. Surfaces are rough, and so they form little microscopic “hills” and “valleys”. Friction is one surface’s hills pushing on the other surface’s hills.

Edit: oh, I see that I really should have read the other responses. @phinds said the same thing but much faster!
 
phinds said:
Yes, it does. It's two rough surfaces sliding over each other with small areas of each sticking into gaps in the other and the surface electrons repel each other. Think of two sawtooth waves "sliding" over each other.
Yes, but as electrons are repelling each other at the molecular level. Similarly, the protons are attracting the electrons of other atoms too. So, u can't say for sure what will be the resultant force between the atoms I mean attractive or repulsive.
 
rahaverhma said:
So, u can't say for sure what will be the resultant force between the atoms I mean attractive or repulsive.
Please don’t use “u” as short for “you” or any other similar text speak shortcuts on this forum.

The resultant force can be calculated using Quantum Mechanics, but it is not simple and involves the Pauli exclusion principle as well as electrostatic and other effects.
 
  • Like
Likes   Reactions: vanhees71