# Solidity

• September 12th, 2010, 02:44 PM
Trev
Solidity
Hi All,

This is probably a basic question (im not a 'scientist') but one ive often wondered about.

Why do objects feel solid and substantial to our touch when physics tells us that all matter is made up mostly of empty space. What is it we are feeling?

Many thanks :-D
• September 12th, 2010, 03:17 PM
jakotaco
The way I got it is that the energy of the particles is increased when matter is compressed. This means it takes a certain amount of work to compress a material, making it feel more or less solid.
• September 12th, 2010, 06:18 PM
Sindrato
When touching an object, what you feel basically is the fraction between atoms of your skin (more precisely the atoms of your nerve endings) and atoms of the table, fore example. In solid things, the atoms are put together in way that uses as much space as possible, due to the shape of the atoms themselves. Try putting boxes on each other so that there is empty space between them, and then press them. Although there is empty space, the boxes themselves are way to big to enter the same empty space. The same thing happens with atoms.
• September 12th, 2010, 10:12 PM
DrRocket
Re: Solidity
Quote:

Originally Posted by Trev
Hi All,

This is probably a basic question (im not a 'scientist') but one ive often wondered about.

Why do objects feel solid and substantial to our touch when physics tells us that all matter is made up mostly of empty space. What is it we are feeling?

Many thanks :-D

You are basically feeling the electrostatic repusion between the electron clouds of the atoms that comprise the the solid materials. There is also a contribution from the Heisenberg uncertainty principle of quantum mechanics.

You can find an accessible discussion of this in The Feynman Lectures on Physics.
• September 13th, 2010, 04:09 PM
jakotaco
Quote:

Originally Posted by Sindrato
When touching an object, what you feel basically is the fraction between atoms of your skin (more precisely the atoms of your nerve endings) and atoms of the table, fore example. In solid things, the atoms are put together in way that uses as much space as possible, due to the shape of the atoms themselves. Try putting boxes on each other so that there is empty space between them, and then press them. Although there is empty space, the boxes themselves are way to big to enter the same empty space. The same thing happens with atoms.

Doesn't sound right, if we wanted to explain it with atoms physically touching each other we would run into trouble considering the incredibly small fraction of the atom that is "solid".

It wouldn't be big boxes with small spaces, it would rather be like a couple of dice spread on Disney World's parking lot.
• September 13th, 2010, 04:30 PM
Sindrato
Of course, you are right. Although we don't yet know quite enough about electrons to be sure are they quite solid. However, I counted on electromagnetic forces to explain the example i posted. If you think of the electron field (or at least the part with noticeable density) as the "solid" atom, than my example stands.
• September 13th, 2010, 06:02 PM
DrRocket
Quote:

Originally Posted by Sindrato
Of course, you are right. Although we don't yet know quite enough about electrons to be sure are they quite solid. However, I counted on electromagnetic forces to explain the example i posted. If you think of the electron field (or at least the part with noticeable density) as the "solid" atom, than my example stands.

You are basically correct, and jackotaco is, as usual, all wet. He can be safely ignored. His next correct observation will be his first one.

When dealing with solids at atomic scales you have to deal with quantum mechanics, and that is a bit different from just dealing with pool balls.

The solidity of solids comes from the electromagnetic forces between electron clouds and the Heisenberg uncertainty principle, which keeps one from squashing the atoms with the electrostatic force.
• September 14th, 2010, 01:26 PM
jakotaco
Quote:

Originally Posted by DrRocket
Quote:

Originally Posted by Sindrato
Of course, you are right. Although we don't yet know quite enough about electrons to be sure are they quite solid. However, I counted on electromagnetic forces to explain the example i posted. If you think of the electron field (or at least the part with noticeable density) as the "solid" atom, than my example stands.

You are basically correct, and jackotaco is, as usual, all wet. He can be safely ignored. His next correct observation will be his first one.

When dealing with solids at atomic scales you have to deal with quantum mechanics, and that is a bit different from just dealing with pool balls.

The solidity of solids comes from the electromagnetic forces between electron clouds and the Heisenberg uncertainty principle, which keeps one from squashing the atoms with the electrostatic force.

So, that is the impression I have given you this far? I would prefer being corrected to being judged like this.

I read Sindrato post as if he was claiming that solidity came from atoms physically touching like pool balls and wanted to point out just how much empty space there is in an atom and that it wouldn't be like stacked boxes.

So what I wanted to say wasn't that atoms acted like pool balls, rather the opposite.

And if your comment was on my first post being incorrect, it may be that I oversimplified or that it was lost in translation, but yes I do know that you have to use quantum mechanics. Sure, I could have said that the eigenvalues of the Hamiltonian is increased as the size of a potential well is decreased and that this is one of the reasons solid objects are solid, but I try to simplify and if something gets lost in translation please point that out so I can fix it instead.
• September 14th, 2010, 11:48 PM
DrRocket
Quote:

Originally Posted by jakotaco
Sure, I could have said that the eigenvalues of the Hamiltonian is increased as the size of a potential well is decreased and that this is one of the reasons solid objects are solid, but I try to simplify and if something gets lost in translation please point that out so I can fix it instead.

Certainly you could have said that.

But it would be just giberish.
• September 15th, 2010, 02:32 AM
jakotaco
Quote:

Originally Posted by DrRocket
Quote:

Originally Posted by jakotaco
Sure, I could have said that the eigenvalues of the Hamiltonian is increased as the size of a potential well is decreased and that this is one of the reasons solid objects are solid, but I try to simplify and if something gets lost in translation please point that out so I can fix it instead.

Certainly you could have said that.

But it would be just giberish.

Gibberish in the sense that it describes a mathematical model without interpreting the results or explaining the physics behind the model, sure it isn't very helpful.

Or do you disagree that the Schroedinger equation predicts that the energy of a confined particle is increased as confinement is made smaller? implying that it takes work to compress such a confinement?

While it is not a full explanation to the stability of matter I would love to hear why you think it is wrong?