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

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Discussion Overview

The discussion revolves around the nature of contact forces, specifically how attractive and repulsive electromagnetic forces contribute to friction and normal reaction forces. Participants explore the theoretical underpinnings and mechanical implications of these forces in various contexts, including the behavior of materials under stress.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that friction is an electromagnetically attractive force while the normal reaction is an electromagnetically repulsive force, expressing confusion over how these different types of forces can combine in contact force.
  • Another participant argues that all forces involved are mechanical forces, emphasizing the interaction of objects pushing against each other.
  • A participant clarifies that while friction does not push, its origin is electromagnetic, and they provide an analogy involving a bridge's structural forces to illustrate that the whole can behave differently than its parts.
  • One participant describes friction as the interaction of rough surfaces, where microscopic features engage with each other, leading to repulsion at the electron level.
  • Another participant elaborates on the complexity of resultant forces at the atomic level, noting that both attractive and repulsive forces are at play, making it difficult to predict the net force between atoms.
  • A later reply mentions that the resultant force can be calculated using Quantum Mechanics, referencing the Pauli exclusion principle and other effects, but acknowledges the complexity involved.

Areas of Agreement / Disagreement

Participants express differing views on the nature of friction and the role of electromagnetic forces in contact forces. There is no consensus on how these forces interact or the implications of their combination.

Contextual Notes

Participants highlight the complexity of the forces involved, including the need for a nuanced understanding of atomic interactions and the limitations of classical mechanics in fully explaining these phenomena.

rahaverhma
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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!
 
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I think you're getting lost in the weeds. They are all mechanical forces of things pushing on things.
 
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.
 
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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.
 
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