Circle/Sphere Touching: Perfection & Friction

[Shropcakes]

Theoretically, if you had a perfect circle, and a perfectly flat surface, wouldn't only one atom touch at a time (assuming friction can't take away the perfect circle/flat surface)? Personally this doesn't sound right, but I can't think of why it wouldn't.

 

[A.T.]

if you had a perfect circle, and a perfectly flat surface, wouldn't only one atom

If they are made from atoms, how can they be perfectly flat or circular?

 

[mrspeedybob]

What do you mean by "touch"? That term does not have a clear meaning at the atomic scale.

 

[Shropcakes]

What do you mean by "touch"? That term does not have a clear meaning at the atomic scale.

As close as possible. I'm not very knowledgeable of physics, so feel free to explain.

 

[Shropcakes]

If they are made from atoms, how can they be perfectly flat or circular?

When I say perfectly round/flat, I mean as round or flat as atoms can get. I understand that because of the electron cloud, the round or flat part can never be the same.

 

[Nugatory]

When I say perfectly round/flat, I mean as round or flat as atoms can get. I understand that because of the electron cloud, the round or flat part can never be the same.

Then you've answered your own question. "As round or flat as atoms can get" is not the same thing as "perfectly exactly geometrically round or flat" so you already know that you cannot reason about this system as if it were perfectly flat and perfectly round.

 

[Shropcakes]

Then you've answered your own question. "As round or flat as atoms can get" is not the same thing as "perfectly exactly geometrically round or flat" so you already know that you cannot reason about this system as if it were perfectly flat and perfectly round.

What is the difference?

 

[davenn]

What is the difference?

reread you own answer in post #5Dave

 

[russ_watters]

So...as round as atoms can get means that on the atomic scale, the circle looks pretty flat, just as the round Earth looks pretty flat to our eyes.

 

[A.T.]

I understand that because of the electron cloud, the round or flat part can never be the same.

If you understand that on the particle level you just have electron clouds, wobbling atoms and varying force fields, then you should see how pointless it is to ask questions based on idealized geometric shapes.

 

[CWatters]

+1

http://sciencequestionswithsurprisinganswers.org/2013/04/16/do-atoms-ever-actually-touch-each-other/

1. If "touching" is taken to mean that two atoms influence each other, then atoms are always touching. Two atoms that are held a mile apart still have their wavefunctions overlapping. The amplitude of one atom's wavefunction at the point where it overlaps with the other atom's center will be ridiculously small if they are a mile apart, but it will not be zero. In principle, two atoms influence each other no matter where they are in the universe because they extend out in all directions. In practice, if two atoms are more than a few nanometers apart, their influence on each other typically becomes so small that it is overshadowed by the influence of closer atoms. Therefore, although two atoms a mile apart may technically be touching (if we define touching as the overlap of atomic wavefunctions), this touching is typically so insignificant that it can be ignored.

 

[A.T.]

+1

http://sciencequestionswithsurprisinganswers.org/2013/04/16/do-atoms-ever-actually-touch-each-other/

There are other possibilities to define "contact", than the three mentioned there. But they might not be generally applicable. See also: