How does weight add up to press on things?

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Discussion Overview

The discussion revolves around the concept of pressure in solids, particularly how weight contributes to the pressure exerted by solid objects on one another at a microscopic level. Participants explore the mechanisms behind this pressure, comparing it to the behavior of gases and examining the role of atomic interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses understanding of gas pressure but struggles with how solid objects exert pressure on each other, questioning the role of atomic interactions when weight is added.
  • Another participant suggests that the force acting on the paper molecules is transmitted through the lower block, implying a connection between the blocks' weights and the pressure exerted.
  • A further inquiry is made about the meaning of "transmitted" in this context, seeking clarification on the microscopic interactions involved.
  • Electromagnetic forces are mentioned as a mechanism for transmission of pressure at the atomic level.
  • It is noted that the repulsion between like charges in atoms is a fundamental reason for the behavior of solids, liquids, and gases, indicating a similarity in atomic interactions across states of matter.

Areas of Agreement / Disagreement

Participants express various viewpoints on the mechanisms of pressure in solids, with some agreement on the role of atomic forces but no consensus on the specifics of how these forces operate microscopically.

Contextual Notes

The discussion does not resolve the complexities of atomic interactions or the precise nature of pressure transmission in solids, leaving several assumptions and definitions open to interpretation.

avorobey
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I think I understand how pressure works with gases. More molecules bouncing around -> more random impacts -> stronger force.

But I realized to my embarrassment that I don't understand how solid things press on each other, microscopically. Say I put a block of iron on my head. If I put another one on top of it, I feel twice the weight. The two blocks together can tear through thin paper where one block can't. But the contact between my head (or paper) and the blocks is just a very thin layer of atoms of the lower block's structure. If the lower block doesn't move when I put the upper one on it, what causes this thin layer to "press" on my head (or paper) more? When the two blocks together tear through thin paper, where does the force come from that acts on the paper molecules - it can't be gravity from the upper block, right? And how come that whatever this source of pressure is only depends on the weight of the upper block, and not on what it's made out of, iron or wood?
 
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avorobey said:
I think I understand how pressure works with gases. More molecules bouncing around -> more random impacts -> stronger force.
To bounce they need some kind of repulsion, right?

avorobey said:
But I realized to my embarrassment that I don't understand how solid things press on each other, microscopically.
The atoms at the boundary also repel each-other.

avorobey said:
When the two blocks together tear through thin paper, where does the force come from that acts on the paper molecules - it can't be gravity from the upper block, right?
Not directly, but transmitted through the lower block

avorobey said:
And how come that whatever this source of pressure is only depends on the weight of the upper block, and not on what it's made out of, iron or wood?
Because that's how pressure is defined: force per area. And the force here depends on weight.
 
>Not directly, but transmitted through the lower block

What exactly does this mean, "transmitted"? Microscopically?
 
avorobey said:
>Not directly, but transmitted through the lower block

What exactly does this mean, "transmitted"? Microscopically?

Electromagnetic forces.
 
Atoms in a solid (or gas or liquid) have electrons on the outside. Like charges repel. Not really any difference between a solid, liquid or gas in that respect. It's why gas molecules bounce off the walls of a vessel rather than disappear into them.
 

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