Sphere on a Flat Plane: 3 Points of Contact?

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    Flat Plane Sphere
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Discussion Overview

The discussion revolves around the contact points between a sphere and a flat plane, exploring the mathematical and physical implications of this interaction. Participants examine whether the number of contact points changes with the size of the sphere and consider the effects of material properties on contact behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that a perfect sphere has only one point of contact with a flat plane, suggesting that this contact area is infinitely small, but raises the question of whether three atoms must touch the plane for the sphere to be at rest.
  • Another participant introduces the idea that at a microscopic level, surfaces are not perfectly smooth, and the interaction may resemble a sponge resting on another sponge, implying that there may not be distinct points of contact due to atomic repulsion.
  • A different perspective suggests that mathematically, a large spherical polyhedron could rest on a flat surface if a triangular face is in contact, indicating that stability can be achieved with different geometrical configurations.
  • One participant emphasizes that the materials of both the sphere and the flat surface will deform, affecting the number of contact points.

Areas of Agreement / Disagreement

Participants express differing views on the nature of contact points, with some focusing on mathematical models while others emphasize physical realities. The discussion remains unresolved regarding the specific number of contact points and the influence of material properties.

Contextual Notes

There are limitations regarding assumptions about the smoothness of surfaces and the definitions of contact points. The discussion does not resolve the mathematical versus physical interpretations of the problem.

Who May Find This Useful

This discussion may be of interest to those exploring concepts in physics, material science, and geometry, particularly in relation to contact mechanics and surface interactions.

CheesyPeeps
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I've been reading about how much of a sphere actually touches a flat plane (spheres are very interesting things, it turns out!). Mathematically, a perfect sphere has only one point of contact, meaning that the area of this contact is infinitely small(?), but as physicists, we know that there must be three points of contact for the sphere to be at rest. Therefore, we can say that three atoms need to touch the flat plane for the sphere to be at rest.

My question is whether this three-atom rule is the same for any size of sphere, or does it change as sphere circumference increases/decreases?
 
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Good question, Mycroft...Hmmmm

(Long story short me and Cheesy Peeps are best friends and this is kinda an in-joke)
 
If you zoom into a billiard ball it won't look very smooth at all. It will look very lumpy. Also you will find that it is not as solid as it appears. So when it is resting on a surface (which will be equally lumpy) zoomed up close it would look more like a sponge resting on another sponge. There will not actually be any points of contact since the repulsive force between electrons in the atoms will keep everything separated. But there will be many close atoms.

On the other hand, if you are talking mathematically, then you can imagine an enormous perfect spherical polyhedron made of triangles. And then mathemat ically it could be at rest if a triangular face lay on the surface of a flat plan. It could also theoretically balance on one or two points but that would be an unstable position.
 
Curious, we had the identical question yesterday.

It depends on the materials of the sphere and the flat surface of course. They will both deform.
 

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