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82
votes
5answers
21k views

What does it mean for two objects to “touch”?

If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of "I'm not actually touching you! The electrons in the atoms of my skin are just ...
11
votes
2answers
883 views

In counting degrees of freedom of a linear molecule, why is rotation about the axis not counted?

I was reading about the equipartition theorem and I got the following quotations from my books: A diatomic molecule like oxygen can rotate about two different axes. But rotation about the axis ...
8
votes
4answers
2k views

Can a single molecule have a temperature?

A show on the weather channel said that as a water molecule ascends in the atmosphere it cools. Does it make sense to talk about the temperature of a single molecule?
131
votes
3answers
17k views

How does a knife cut things at the atomic level?

As the title says. It is common sense that sharp things cut, but how do they work at the atomical level?
5
votes
4answers
8k views

Water in vacuum (or space) and temperature in space

So, water in vacuum will boil first and then freeze. I don't know how the freeze happens. As pressure lowers to zero, what happened to freezing point? (I know heat taken by vapor, and the water cool ...
6
votes
1answer
6k views

Why does a breeze of wind make us feel cooler? [duplicate]

In my Astronomy class, I learned that temperature results from the speed of air molecules colliding into your skin. Thus, if the air molecules in the room have a high kinetic energy and thus collide ...
8
votes
2answers
1k views

The distance between touching objects

What is the distance between, say, a cup of coffee and the table it rests on? What is the distance between two touching hands?
2
votes
3answers
2k views

Is the molecule of hot water heavier than that of cold water?

We know that the molecule of hot water($H_2O$) has more energy than that of cold water (temperature = energy) and according to Einstein relation $E=mc^2$ ,this extra energy of the hot molecule has a ...
1
vote
1answer
10k views

What's the size of carbon dioxide? [closed]

My question is very simple. How big is a carbon dioxide ($\mathrm{CO}_2$) molecule, i.e. the width, length and height of it?
0
votes
3answers
1k views

Potential energy curve for intermolecular distance

I'm trying to understand this curve better, but I can't quite figure out what "negative potential energy" means. The graph should describe a molecule oscillating between $A$ and $B$, however where I'...
8
votes
1answer
234 views

Are Born-Oppenheimer energies analytic functions of nuclear positions?

I am looking for references to bibliography that explores the smoothness and analyticity of eigenvalues and eigenfunctions (and matrix elements in general) of a hamiltonian that depends on some ...
6
votes
3answers
9k views

What is the resonant frequency of liquid water?

I learned it's not 2.45 GHz. But what is it, then? In my failure to find the real value, I'm starting to wonder: does it even make sense talking about a resonant frequency of water molecules?
15
votes
3answers
2k views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
8
votes
4answers
1k views

Hot water freezing faster than cold water

This question has puzzled me for a long time. There is already a question like this on Physics.SE. John's answer to the question seems quite satisfying. But when I googled the cause I found this and ...
3
votes
1answer
124 views

Relative weights in rotational bands of symmetric diatomic molecules

In an old paper, Ehrenfest 1931, the introduction starts off as follows: The band spectra of symmetric diatomic molecules show certain striking differences from those of asymmetric molecules. For ...
3
votes
2answers
76 views

During the “Dark Ages” of the Universe's evolution, how lumpy (anisotropic) and dynamic was the mass distribution?

In the dark ages between recombination (~0.4 Myr post-BB) and reionization (~300 Myr post-BB) of atoms, there was not any condensed-phase matter (except maybe some form of dark matter), nor radiation ...
2
votes
3answers
657 views

How do the molecules of reacting compounds proceed to form “Most Stable” molecule?

This question is a cross post from chemistry. I'm not very convinced with the answer there. So, I'm posting it here. I'm tutoring few students for Chemistry. During the course, I many times use the ...
2
votes
2answers
202 views

How do atoms in a solid “communicate” force to each other?

What is the mechanism that carries and communicates force in a solid, on the atomic level? Is there some other mechanism besides atomic deformation and proximity? That is, if I had an infinitely ...