Solid objects do not actually vibrate, correct?

Question

I know atoms and molecules that make up a solid vibrate, but does the solid object itself actually vibrate?

Answer 1

Hi Hailey P.,

An interesting question asked on Wyzant, for a change! I welcome interesting questions.

So -- you know that the individual particles have suppressed translational motion, which they can only express by wiggling in place. (Unless they are heated a bit; then they diffuse slowly, for example metal atoms in a block of metal. But it's macroscopically very slow, though it leads to such things as creep, annealing, grain boundary movement, etc.) So, how you measure motion is critical here. The tool you might use to observe a phonon of vibration (look that up!) in the bulk solid (some spectroscopic technique, or an atomic force probe, perhaps) isn't what you would need to observe the whole solid as a block. Solids just sit there: the surface particles of the solid and of the support or measurement tool are bonking against each other continuously, but the contacts are so numerous that the net result is fairly constant (the measured mass of a block doesn't fluctuate much due to varying vibration against the pan; even the empty pan doesn't vary due to irregular (but statistically predictable) strikes of air molecules).

So, yes, there is local "wiggle", but, overall, you don't see that as a motion of a chunk of solid, even if you squint hard! Except when you get down to nanometer sizes (then other things of interest happen than just translation or vibration at quantum scales); even microscopic sized particles are bounced around by Brownian motion; but we deem that due to the molecules of the liquid (or fluid) hitting the solid particles, even though obviously each collision requires 2 particles, so why is one considered "the hitter" and the other "the hittee"? I think that's a bit of prejudice due to the solid being visible, whereas the liquid molecules aren't (in general).

-- Cheers, --Mr. d.

Answer 2

Hi Hailey, this is a great question. Atoms reach their minimum vibration state at absolute zero (0 degrees Kelvin, -273.15 degrees Celsius). Even at these extremely low temperatures (lowest possible kinetic energy of a substance) particles remain in motion due to the Heisenberg uncertainty principle. So, atoms and molecules comprising matter in solid state will vibrate even though the object they build appears motionless.

Unlike a liquid or gas, however, the particles in solids maintain a fixed position. It's only as energy is applied to the object (e.g., heat) that the particles' movement increases until they break away from their fixed position and experience a change of state.

In summary, the solid object does not vibrate but stays in a fixed position because the particles comprising the solid are fixed in place.

I hope this helped! If you want to learn more, here are some helpful links:

Explanation of Heisenberg Uncertainty Principle:

https://scienceexchange.caltech.edu/topics/quantum-science-explained/uncertainty-principle#:~:text=Formulated%20by%20the%20German%20physicist,about%20its%20speed%20and%20vice

States of Matter Explained:

https://courses.lumenlearning.com/suny-earthscience/chapter/states-of-matter/