when something touches what is actually touching?

[R1Geezer]

Eg take 2 snooker balls when we can see they are "touching", what is actually touching at a microscopic level? I mean we know that atoms are a nucleus surrounded by huge empty space with electrons orbiting. So when 2 snooker balls, ie fairly solid surface, touch at what point to they actually touch, ie you can feel they are touching, do the orbits of the electrons overlap somehow or is the nuclear force stopping integration.

[jake-the-peg]

No an atom is not a nucleus with electrons orbiting. That's a simplified version that's easier to teach. The electron shells are effectively a probability distribution where there's a certain probability of finding an electron any time you look. So it's more of a cloud than an orbit.

The electrons repel each other via the electromagnetic force (not the nuclear force), again probability will come into play as they get closer and closer there's an increasing probability that they will exchange virtual photons which "mediate" the electromagnetic force.

So in a sense the contact is "spongey" but the distances we are talking about between no contact and contact are so small that the spongeyness is hidden from us.

When electron "orbits" "overlap" that is a covalent chemical bond of the type that joins say Sodium and Chlorine in a salt molecule

[R1Geezer]

thanks Jake, excellent answer.

[vascop]

It might be an excellent answer, but does it answer the question? I don't think so - not for me anyway. Sounds like a politicians answer.

[jake-the-peg]

In what way vascop?

I'm sorry there's an element of probability in there - if you don't like it you're in good company Einstein spent thelast years of his life fruitlessly trying to show quantum mechanics and probability was wrong.

He failed of course and QM is pretty much the best verified "theory" in all of physics

But if that's the bit you don't like I can sympathise

[jno]

Zacsmaster, yes, I often find myself wishing Jake had taught me physics at school instead of the clot who did. 50 years too late now, unfortunately.

[R1Geezer]

I am satisfied with Jake's answer vascop, but that may be because I do have a pretty good understanding of the area myself and just need the occassional gap filling. I know jake has excellent knowledge in the area. What else would you like to know? What is left unexplained?

[vascop]

Jake
I'm happy with the probability bit. I studied QM at university many moons ago. It's just that I'm still not sure what,at the atomic level, is actually making the billiard balls so hard and say two balls of dough so soft.

[beso]

You might be interested in reading about the Atomic Force Microscope which measures surfaces at atomic resolution by poking them with a sharp point.

http://en.wikipedia.o...omic_force_microscope

[Old_Geezer]

So if anything touches, it the electromagnetic forces. The constituent bits of an atom tend to remain pushed apart (unless you force them to smash into each other I guess, and get showers of new particles; or in a neutron star :-) ).

Dough is more able to deform than a billiard ball is so its molecules will move over each other making its surface soft.