Longitudinal wave speed

[brood910]

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I know that the speed of longitudinal wave is equal to square rt of YP/density.
I also know that v in solid > v in liquid > in gas.
These two concepts work very well together when we consider water (the density of liquid water is higher than that of solid water).

However, for other objects, the density of liquid is usually lower than that of solid.
This will make the two concepts above go against each other (the formula says speed in liquid is faster than that in solid)..

So, my question is, if the medium is not water, which concept comes first?

 

[reising1]

I know that the speed of longitudinal wave is equal to square rt of YP/density.

I'm not sure what this formula is and I don't think it's necessary for the MCAT. Wave velocity is best known as v = lambda*frequency for MCAT.

This rule should always prevail:
For light, density slows waves down.
For sound, density speeds waves up.

For something that is both hot and dense, for example, the speed increase (from temperature) and speed decrease (from density) of a light wave would seem to cancel out in a way, but that's just a guess.

 

[brood910]

I'm not sure what this formula is and I don't think it's necessary for the MCAT. Wave velocity is best known as v = lambda*frequency for MCAT.

This rule should always prevail:
For light, density slows waves down.
For sound, density speeds waves up.

For something that is both hot and dense, for example, the speed increase (from temperature) and speed decrease (from density) of a light wave would seem to cancel out in a way, but that's just a guess.

That is for transverse (ex: light), not longitudinal.
Also, no. Since sound is longitudinal wave, density slows down the wave.

 

[dcamkl1]

Your formula generally works for gaseous media.

For comparing the speed of sound between two different phases or medium, you have to consider the restoring force and kinetic energy (Temp). Specifically, speed of sound (v) is proportional the square root of the restoring force or molecular kinetic energy.

 

[brood910]

Your formula generally works for gaseous media.

For comparing the speed of sound between two different phases or medium, you have to consider the restoring force and kinetic energy (Temp). Specifically, speed of sound (v) is proportional the square root of the restoring force or molecular kinetic energy.

Wow.. Cant believe that I missed that part in the book. Thanks a bunch.
So, does V of sound = sqr rt of KE/molecular intertia work in ALL media?

 

[dcamkl1]

Wow.. Cant believe that I missed that part in the book. Thanks a bunch.
So, does V of sound = sqr rt of KE/molecular intertia work in ALL media?

Yes, I think so. Increasing the temperature means you are increasing the kinetic energy, so that would satisfy both formulas; molecular inertia is the same as mass density (according to TBR), and again that satisfies both formulas. It's just that in a gaseous medium, you have to consider other factors like pressure and type of gas (monoatomic, diatomic, etc.)