Why Do Molecules Move?

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Hootenanny

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prj45 said:
So, what would happen if I had a single molecule in a perfect vaccum, and introduced a single photon, and that photon was absorbed by one of the atoms in the molecule?

Would the molecule move?
I would suggest you read my above post. This concerns an isolated CO2 molecule which absorbs a photon of visible light.
 

DaveC426913

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prj45 said:
So, what would happen if I had a single molecule in a perfect vaccum, and introduced a single photon, and that photon was absorbed by one of the atoms in the molecule?

Would the molecule move?
A couple of things to consider:
1] The molecule will have an initial amount of vibrational energy. Bonds vibrate laterally, radially and rotationally.
2] The molecule will have an initial amount of kinetic energy.
Neither of those two can you eliminate in your experiment.

Now, given the above, and given that your one photon was absorbed by your molecule, the answer is yes, its kinetic energy would change. Yes, it would move.
 
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DaveC426913 said:
1] The molecule will have an initial amount of vibrational energy. Bonds vibrate laterally, radially and rotationally.
2] The molecule will have an initial amount of kinetic energy.
Neither of those two can you eliminate in your experiment.
You could turn the temperature down...
 
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Thanks for your input guys.

I guess what I don't get, is what is happening when a photon meets an molecule. Or let's keep it simple and say an electron. Which is related to the fact that I can only guess at what a photon is, and what an electron is.
 

Hootenanny

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masudr said:
You could turn the temperature down...
Even at zero kelvin there would still be some movement.
 

Hootenanny

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Farsight said:
Thanks for your input guys.

I guess what I don't get, is what is happening when a photon meets an molecule. Or let's keep it simple and say an electron. Which is related to the fact that I can only guess at what a photon is, and what an electron is.
If you do not want to go into things too deeply,you can just think of a photon as a particle, it carried kinetic energy and momentum, just think of it as a moving particle (photon) colliding with a stationary particle.
 
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Yup, thanks everyone, v interesting.

I'll not ask what started all this movement off in the first place... :p
 
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Hootenanny said:
If you do not want to go into things too deeply,you can just think of a photon as a particle....
I do want to get into it more deeply, Hooteney. Particles are giving me a big problem at the moment. I just can't see a photon as a particle any more. It seems more like an action - I don't know, a punch, a whiplash, a shout, a ripple with no pinpoint location and any size you like. And an electron seems like some kind of standing wave onion ring ripple. I'm somewhat driven by the search for concepts here.
 

ZapperZ

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Farsight said:
I do want to get into it more deeply, Hooteney. Particles are giving me a big problem at the moment. I just can't see a photon as a particle any more. It seems more like an action - I don't know, a punch, a whiplash, a shout, a ripple with no pinpoint location and any size you like. And an electron seems like some kind of standing wave onion ring ripple. I'm somewhat driven by the search for concepts here.
In all your postings, you seem to have ignored one other possibility - that the concept that you are using such as "particle" may be the one at fault!

It is very possible that the property of "particle" may have no relevancy at such a scale. So trying to force something like a photon or an electron to have a particle property is like trying to force a square object through a round hole. When it doesn't fit, you blame the square object. Why not also blame the round hole? You are trying to force two incompatible concept together that may or may not work.

Electrons can, under classical conditions, be thought of as classical particles. People working in particle accelerators use this all the time to excellent accuracy. Photons can be thought of as clumps of energy. That model has worked everywhere. So let's leave it at that, rather than trying to dress it with properties that it wasn't meant to have in the first place.

Zz.
 

Astronuc

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Farsight said:
I guess what I don't get, is what is happening when a photon meets an molecule. Or let's keep it simple and say an electron. Which is related to the fact that I can only guess at what a photon is, and what an electron is.
Well, it depends on the energy (wavelength/frequency) of the photon. First of all, molecules are composition particles, and they are three dimensional. They can translate, rotate and vibrate at different characteristic frequencies (corresponding to different energy states). In addition, some (many) molecules have charge asymmetries leading to a dipole moment.

The interaction of the photon depends upon whether or not that photon matches any one of many characteristic frequencies. In some cases, a photon may just simply pass right pass or 'through' the molecule with little interaction. On the other hand, if not absorbed in some excitation process, the photon will be scattered - redirected.

Photons and electrons exhibit both particle and wave behavior. Particle in the sense of being 'localized' or 'quanitized', and wave in the sense of collective behavior, e.g. interference.

How do know this? By experiment and observation.

We observe the Universe/Nature in which we exist. We use mathematics and physics to try to describe, explain and understand what we observe. Sometimes we can accurately describe the behavior we observe, and others time not. In the end, the Universe/Nature is what it is, and the challenge is to understand it, and even appreciate it, in the limited time of our existence. :smile:
 
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ZapperZ said:
...the concept that you are using such as "particle" may be the one at fault...
Oh, most definitely Zapper. I think "particle" has caused a whole heap of problems.

Thanks for trying Astronuc.
 
Don't just quit! Now it's getting interesting. Electrons and any other charged particles are moved by electromagnetic and other fields, oscillating and non-oscillating, fields - and there are plenty around in space and vacuum. We all seem to be victims of Dr. Brown's observation of pollen quivering on the surface of a drop of water under his microscope as a result of the surrounding irregular bombardment by by water molecules. What a nonsense when you consider the difference of mass between an oscillating water molecule and the asteroidal mass of the pollen it pounces on. Then consider the zillions of water molecules in the immediate boundary layer of water enveloping the pollen. Then consider Stokes' law which would prohibit the small pollen particle to move at the observed speed through water. Then submerse a 0.8 micrometer diameter particle in water and observe its random motion "through" the water vehicle. Its velocity is now so much faster than that of the much larger pollen, thus defying Stokes' law even more. Our pool ball collision kinetics seems to be totally outdated.

Now, what kicks the molecule off your 0 K pedestal, accelerates it from zero to meters per second speed for ever if nothing else bumps into it? If we feed it with the photon's energy, why would this energy have to manifest itself as kinetic energy in the molecule and not in any other form of energy? I would say, the molecule would simply stay on its pedestal and enjoy the swallowed energy from the photon as potential energy. Period.

Why do molecules move? They follow field gradients. The field quiver.
 

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