Confused about speed of sound dependence on density

[deleted647690]

From the equation, v = square root of bulk modulus / density, I would think that as the density of an object increases, its speed decreases. This is in contradiction with the idea that the speed of sound is faster in solids > liquids > gases. I mean I guess you also need to consider the bulk modulus.

Also, there is a question in TBR, "When an ultrasonic wave goes from air to tissue, what is true?"

They said that the wave speed increases because the density of the medium has increased. They also said, "As a general rule, when an ultrasonic wave (any sound wave) goes from a less dense medium to a denser medium, it increases in speed." This also contradicts the equation above....Is this beyond the scope of the MCAT?

---

Members don't see this ad.

 

[Nugester]

It's not really in contradiction. Reason V(s)>V(l)>V(g) is because of bulk modulus. There are stronger intermolecular bonds from (s) > (l) > (g) so the bulk modulus decreases from (s) to (l) to (g). Meaning, things are propagated faster when things are closer together (due to bonds in (s) & (l) as opposed to (g) which are furtherest apart).

As for your second question, if it goes from air to tissue, wave speed increases. I don't agree withthe last part. If it goes to a denser medium, speed DECREASES. I think it might have meant that if it goes into an increasingly STIFFER medium, speed increases.