csx

May 8, 2013
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exhibits:
A) High resistance to compression and low density
or
B) Low resistance to compression and low density

the answer is B. i dont get why. I figured if the sound hit a medium which has a high resistance to compression and low density it would be less likely to compress (harder to compress and molecules less 'tight' cuz low density so spread out more)...

I dont get why B is the answer.
 

popopopop

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Dec 18, 2011
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Can you check your answer again to make sure? From what I understand, v= (B/p)^.5 where B = bulk modulus of elasticity and p is density. So low density works, but high resistance to compression should give us a faster velocity. Of course, if someone knows the flaw in this, please correct us :).
 
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csx

csx

May 8, 2013
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v=Sqrt(Bulk modulus/density), we expect low v when b is low and density is high.
 
Last edited:

Hadi7183

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Ah, I'm confusing myself. This is right - the question asks in which media the speed is SLOWER. Lower resistance --> smaller B --> slower speed.
 
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csx

csx

May 8, 2013
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Lol, whoops, yep, slowest.
wouldnt a (equation aside) intuitively speaking wouldn't having a high resistance to compression (rather than a low one) impede sound??
 

popopopop

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^Good summary below.

"
At the particle level, a rigid material is characterized by atoms and/or molecules with strong forces of attraction for each other. These forces can be thought of as springs that control how quickly the particles return to their original positions. Particles that return to their resting position quickly are ready to move again more quickly, and thus they can vibrate at higher speeds. Therefore, sound can travel faster through mediums with higher elastic properties (like steel) than it can through solids like rubber, which have lower elastic properties.

The phase of matter has a large impact upon the elastic properties of a medium. In general, the bond strength between particles is strongest in solid materials and is weakest in the gaseous state. As a result, sound waves travel faster in solids than in liquids, and faster in liquids than in gasses. While the density of a medium also affects the speed of sound, the elastic properties have a greater influence on the wave speed."

https://www.nde-ed.org/EducationResources/HighSchool/Sound/speedinmaterials.htm