# Thread: Vibrations in States of Matter

1. So i have a question. I know that when you heat up a solid to a certain temperature, the molecules move faster, causing it to melt. Well, would it be possible to melt something using Vibrations without any heat? Could it be possible to make the molecules move fast enough to change states using, say an extremely high frequency of sound? Thanks

2.

3. Put Cheese in the microwave

4. Originally Posted by knightx4
So i have a question. I know that when you heat up a solid to a certain temperature, the molecules move faster, causing it to melt. Well, would it be possible to melt something using Vibrations without any heat?
Congratulations!
You've invented the microwave oven.
I would patent the idea before someone else thinks of it.

5. Originally Posted by knightx4
So i have a question. I know that when you heat up a solid to a certain temperature, the molecules move faster, causing it to melt. Well, would it be possible to melt something using Vibrations without any heat? Could it be possible to make the molecules move fast enough to change states using, say an extremely high frequency of sound? Thanks
If you blast a lot of energy - in just about any form, including sound - at something, you will find it heats up, in proportion to the degree to which the energy is absorbed. Other respondents have concentrated on the microwave oven, which uses microwave electromagnetic radiation to stimulate rotation of water molecules - which is then randomised by molecular collisions into general heating of the object.

A blast of sound may or may not be absorbed. If it is not, then the object will transmit the sound and won't heat up. The sound waves hitting the object make it vibrate in sympathy, the sound wave propagates through the object and out the other side. But something that absorbs the sound will just get hotter.

As to frequency of the sound, it is going to be impossible to make a sound wave with a frequency high enough to be comparable to the frequency of a vibrating atom: you won't be able to make a bulk object move macroscopically with such a frequency. If you did, then instead of generating a sound, it would just get hot!

6. Technically, at least in an ideal world if not the real world, it is possible to impart energy to a crystalline state without heating it. Usually, the equipartition principle causes energy in one mode to distribute equally among the other modes, ultimately increasing the temperature. However, in a system where the energy modes are exactly normal to each other, energy cannot be transferred from one mode to another, and the equipartition principle fails.

7. Originally Posted by KJW
Technically, at least in an ideal world if not the real world, it is possible to impart energy to a crystalline state without heating it. Usually, the equipartition principle causes energy in one mode to distribute equally among the other modes, ultimately increasing the temperature. However, in a system where the energy modes are exactly normal to each other, energy cannot be transferred from one mode to another, and the equipartition principle fails.
I suppose that's right. But how would you excite a single lattice vibration mode?

8. Originally Posted by knightx4
So i have a question. I know that when you heat up a solid to a certain temperature, the molecules move faster, causing it to melt. Well, would it be possible to melt something using Vibrations without any heat? Could it be possible to make the molecules move fast enough to change states using, say an extremely high frequency of sound? Thanks
Atomic molecular vibrations within an object can produce EM radiation which defines heat. Any kind of exterior radiation that can be absorbed like sound, ultra-sound, micro-waves, EM radiation, can produce heat in an adjacent object.

9. Originally Posted by exchemist
Originally Posted by KJW
Technically, at least in an ideal world if not the real world, it is possible to impart energy to a crystalline state without heating it. Usually, the equipartition principle causes energy in one mode to distribute equally among the other modes, ultimately increasing the temperature. However, in a system where the energy modes are exactly normal to each other, energy cannot be transferred from one mode to another, and the equipartition principle fails.
I suppose that's right. But how would you excite a single lattice vibration mode?
Resonance. I suppose phonons in a crystal lattice would be the best opportunity to produce excitations that don't heat the material, and diamond would probably be the optimum material (although the OP referred to melting the material this way). Different excitation modes (of any system) are normal, but randomising influences can transfer energy from one mode to another. For example, the different bond vibration modes of isolated molecules are normal, but if the molecules are not isolated from each other, then random collisions can transfer energy between the molecules and between the excitation modes (spectral lines in the liquid phase are usually much broader than their gas phase counterparts). For a crystal of a typical organic molecule, the individual molecules have relatively high internal degrees of freedom which would allow collisions between neighbouring molecules to transfer energy between the excitation modes of the lattice vibrations. Thus, one should choose a crystal of a substance with few if any internal degrees of freedom.

10. Generally speaking, the statement that energy can't be transferred from one normal mode to another assumes linearity.

11. Originally Posted by KJW
Originally Posted by exchemist
Originally Posted by KJW
Technically, at least in an ideal world if not the real world, it is possible to impart energy to a crystalline state without heating it. Usually, the equipartition principle causes energy in one mode to distribute equally among the other modes, ultimately increasing the temperature. However, in a system where the energy modes are exactly normal to each other, energy cannot be transferred from one mode to another, and the equipartition principle fails.
I suppose that's right. But how would you excite a single lattice vibration mode?
Resonance. I suppose phonons in a crystal lattice would be the best opportunity to produce excitations that don't heat the material, and diamond would probably be the optimum material (although the OP referred to melting the material this way). Different excitation modes (of any system) are normal, but randomising influences can transfer energy from one mode to another. For example, the different bond vibration modes of isolated molecules are normal, but if the molecules are not isolated from each other, then random collisions can transfer energy between the molecules and between the excitation modes (spectral lines in the liquid phase are usually much broader than their gas phase counterparts). For a crystal of a typical organic molecule, the individual molecules have relatively high internal degrees of freedom which would allow collisions between neighbouring molecules to transfer energy between the excitation modes of the lattice vibrations. Thus, one should choose a crystal of a substance with few if any internal degrees of freedom.
Interesting. But how would you excite the chosen vibrational mode, in such a case? One can use a photon of appropriate frequency to excite a chosen electronic, vibrational or rotational excitation of an atom or molecule, but what means does one use to excite a single mode of lattice vibration? Is there an IR absorption frequency for a lattice vibration? If not, how does one do it?