Stiffness versus elasticity

[Tokspor]

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Regarding sound waves, in EK Physics, the text on page 99 says that "heavier mediums tend to slow waves down, while stiffer mediums tend to speed waves up." But it then says that a medium's resistance to motion will slow down the waves while an elastic medium will speed them up.

The information about "resistance to motion" and "elasticity" make sense to me. But the information about the "heaviness" of the medium does not, and the information about "stiffer" mediums seems contradictory to elasticity.

For heaviness, would they be talking about density? I think that sound waves propagate faster in denser and more elastic mediums. As for stiffness, how would this speed up sound waves, even when it's stated that they travel faster in elastic mediums?

 

[Tokspor]

bump

 

[inaccensa]

Regarding sound waves, in EK Physics, the text on page 99 says that "heavier mediums tend to slow waves down, while stiffer mediums tend to speed waves up." But it then says that a medium's resistance to motion will slow down the waves while an elastic medium will speed them up.

The information about "resistance to motion" and "elasticity" make sense to me. But the information about the "heaviness" of the medium does not, and the information about "stiffer" mediums seems contradictory to elasticity.

For heaviness, would they be talking about density? I think that sound waves propagate faster in denser and more elastic mediums. As for stiffness, how would this speed up sound waves, even when it's stated that they travel faster in elastic mediums?

If I remember correctly, we are talking about the inertial and elastic component. Inertia is resistance to motion and Elastic is resistance to shape. The reason that waves move faster in solids than in gases, despite the fact that their inertial component, resistance to motion greater than that of gases is simply cause their elastic component is supersedes the inertial component. Ex-Heavier medium with lets say greater density. If you compare two liquids with same bulk modulus and different density, the one with greater density will obviously decrease the speed. remember the equation B/d ^1/2

remember that elastic component is more imp than the inertial component.

If you take the same 2 liquids but if the increase the bulk modulus of the one with lower density, the wave will move faster in that medium. This is how i understand it.

 

[inaccensa]

Just wanted to add more abt Elastic component. i was getting a lil confused too😳

Modulus = F/A
change in dimensions.

If the denominator is a small #, the modulus will be a larger #
this implies that the medium is resistant to change in shape, it is stiffer!!

In your speed formula Modulus/ inertial component. If your numerator goes up, the speed will increase.

 

[Tokspor]

So if we compare the speed of sound in the following three mediums: air, water, glass, would it be glass > water > air since the stiffness is more important than the density?

 

[inaccensa]

So if we compare the speed of sound in the following three mediums: air, water, glass, would it be glass > water > air since the stiffness is more important than the density?

that is correct. Check out the speeds
http://hypertextbook.com/physics/waves/sound/