Do molecules in a solid object move?

[Guest nicora]

Do molecules in a solid object move?

 

I thought that molecules in a solid object still move, but very slowly, only to stop once freezed. Then I read this

 

"A secondary characteristic of a solid is that no matter how hard it is squeezed or pulled, the molecules do not move closer together or further apart."

 

Is this true? And could you possibly attach proof for the correct answer?

 

Thanks in advance!

[fafalone]

Molecular movement is related to temperature; not state. The molecules in all solids are moving, and molecular movement only stops at absolute zero (0 Kelvin).

[Guest nicora]

Thanks for that, and sorry to post such a remedial question. But I have one more

 

Are molecules moving faster in solids vs. gases and liquids? or just further apart?

[VendingMenace]

Do molecules in a solid object move?

 

yuppers, they move, but more on this is just a bit

 

I thought that molecules in a solid object still move, but very slowly, only to stop once freezed. Then I read this

 

"A secondary characteristic of a solid is that no matter how hard it is squeezed or pulled, the molecules do not move closer together or further apart."

 

This quote is not really true. The truth is that it is extremely hard to change the intermolecular distances between molecules in a solid, and most liquids. This is why we say that gasses do not have a set volume, while liquids and solids do. Liquids and solids are said to have a set volume per unit mass (or a characteristic density) and as such they are mostly treated as if you could not squeeze the individual molecules closer together.

 

However, if you squeezed really really hard, you could change the density of a solid. Like if you were to but graphite under alot of pressure, it would change density and we would call it a dimond.

 

This is a bit simplistic of an explination, but i think the idea is clear. If you take issue with this explination or want more, then just ask

 

 

Now about molecules moving in a solid. Molecules DO, in fact, move in a solid. Molecules are constantly vibrating, rotating, and moving from one spot to another (translational movement). In a solid, translational movement is inhibited alot. So much so that molecules in solids generally do not just move about. They are fixed in one spot within the solid. However, they still do vibrate. And as such, they still have motion.

 

Molecular movement is related to temperature; not state. The molecules in all solids are moving, and molecular movement only stops at absolute zero (0 Kelvin).

 

Translational movement stops at 0k, not moleculare movement. The molecules are still vibrating. What happens at 0k is that a molecule is in its lowest possible quantum state. But it is still moving. The molecule could not stop moving completely, or it would violate the generalized uncertainty priciple.

 

 

Are molecules moving faster in solids vs. gases and liquids? or just further apart?

 

Well, the definition of solid vs gas just tells us that the molecules are farther apart. It tells us nothing about the relative speeds. In order to calculate the speed of a molecule you would need to know what amount of kenetic energy the molecule has and what its mass is. In order to do this we take the molecules temperature, for temperature is just a measure of average kenetic energy. Then we find the molecules mass and we can determine its speed.

 

But to answer your question. Given an unknown solid and an unknown gas all we could say about them is that the molecules in the gas are father apart than the molecules in the solid. We really cannot say anything about relative speed of the molecules in the gas vs. those in the solid.

 

 

HOpe that answers your qeustions, feel free to ask more

[Guest nicora]

Well, that was a fantastic reply, and thank you very much for the response. I have had one slightly contridicting statement elsewhere. Could you tell me if it holds any ground? Or is it just a matter a preception about the english langauge...

 

"Even the most elementary of scientists recognizes that in a solid, the energy level of the molecule is too low to allow them to escape their combined fields of attraction such that every molecule is essentially permanently trapped amid fixed neighbors. Furthermore while not entirely motionless, their motion is therefore restricted to vibration about a fixed position. So in conclusion solids are not moving, rather the individual molecules that comprise my desk are independently vibrating."

[Guest nicora]

I didn't replace the terms correctly, read the below quote instead. Sorry :lame:

 

 

""Even the most elementary of scientists recognizes that in a solid, the energy level of the molecule is too low to allow them to escape their combined fields of attraction such that every molecule is essentially permanently trapped amid fixed neighbors. Furthermore while not entirely motionless, their motion is therefore restricted to vibration about a fixed position. So in conclusion solids are not moving, rather the individual molecules that comprise a solid are independently vibrating." "

[aman]

We all have seen that hydraulics use liquids to distribute forces due to the fact that fluids are not compressable. As far as solids go, here is an interesting example of metals surrounded by heat and a balanced powerful external explosion at the same time.

 

small coins

 

The most you can compress a solid is into a sphere but it will never change its density.

Just aman

[VendingMenace]

sup nicora,

 

i don't see anything wrong with the quote that you supplied, but lets look at it in parts

 

the energy level of the molecule is too low to allow them to escape their combined fields of attraction such that every molecule is essentially permanently trapped amid fixed neighbors

 

Yeah, this is correct. Essentially, what you are doing when you melt something is to supply enough kenetic energy to the molecules that they break the force of attacktion with their neighbors that holds then in their fixed posioin (this ordered, rigid, posision of molecules in a solid is known as the "lattice"). Thus, the molecules are free to move around , or flow, about eachother and the substance has made the transition from solid to liquid.

 

If you continue to heat the substance, eventually, the molecules will have enough energy to not only move around freely, but to fly away from eachother. In this case, the liquid trasitions into a gas.

 

Furthermore while not entirely motionless, their motion is therefore restricted to vibration about a fixed position.

 

yeah, this is correct again. In a solid, molecules are held in a fixedc position within the solid's lattice. They are not free to move about in space (or at least their movement is severely restricted). However, the individual molecules still undergo vibrations. So, while the molecules are still techincally moving, their acerage position in space does not change. As an example of this, consider a piano string. When it is struck, it vibrates. Hence it is moving. However, the string does not really go anywhere. It stays in its fixed position within the piano, despite the fact that when it is vibrating it is in motion.

 

I hope that makes sense

 

So in conclusion solids are not moving, rather the individual molecules that comprise a solid are independently vibrating

 

Ok, so what is being said here is that, despite the fact that the molecules within the solid are clearly moving (undergoing vibrations), the solid as a whole is viewed as a static object. That is, although the molecules within the solid are constantly in motion, the solid itself does not jump about on a table, nor does it randomly change shape.

 

This is clearly seen evereday. If we were to put a brick on a table, the brick would neither change shape, nor would it move without something else moving it. HOWEVER, the individual molecules within the brick are quite dynamic, and are constantly in motion. It just happens that they are fixed fairly well in space, and so we can see that the brick has a definite shape to it.

 

Yeah, so i hope that helps some more. Again, feel free to ask more questions

[aman]

I reread my post above and then thought about solid carbon being compressed into a diamond. I guess I have to qualify my argument because under exteme pressures and temperatures, a lot of solids could potentially have their density changed at an elemental level. Just toss it in a black hole.

But the general rule, with exeptions, is they are not compressable.

Just aman

[VendingMenace]

true

 

and really it all depends on what you are talking about. If you are saying that graphite cannot be compressed, then you are correct, becuase once the carbon starts compressing, it is no longer graphite. It has become diamond.

 

As another (and probably better) example, we can look at the different phases of ice. You can compress ice and it will go through phase changes to more dense phases of ice. HOwever, these are discrete changes and not the smooth compression that we usually think of when talking about gasses.

 

So, you are most certainly correct. Solids (and liquids), as a general rule, cannot be compressed. The point that i was trying to make is this...their rigidity is just do to latice forces that hold the molecules in fixed places. These forces, like almost every other force, can be overcome. Thus, you CAN compress a solid, given enough pressure. The compressed solid remains a solid, however, it may change other properties, and, as such, perhaps it is not really what we shoud properly think of as compression.

 

I suppose that i was just trying to point out that the latice forces could be overcome, and i used a poor choice of non-techinal terms to convey this. sigh...oh well, i guess we can't be precise all the time