Speed of sound in water

[Raiden2012]

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A pinging device, producing sound at 300 Hz, is submerged in 30°C water. As the water is cooled to 4°C water (the temperature at which water is the most dense):


would the speed increase or decrease?

 

[Raiden2012]

My answer was that the speed would decrease due to the increased density. Since EK said speed decreases with increasing density and increases with incompressibility.

However, the answer to this question was speed increases because of higher density. So I am getting confused? Does speed increase with density or not?

 

[Ansar]

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe2.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe2.html#c2

I'd wager that the EK answer is wrong.

 

[Raiden2012]

Thanks. Btw what do the korean words in your sig mean? Something to do with curry?

 

[BB8730]

However, the answer to this question was speed increases because of higher density.

That answer is incorrect. In the same medium, sound travels faster as temperature increases. When the molecules of the medium have a higher temperature, they can vibrate faster and thus transmit sound faster.

http://www.engineeringtoolbox.com/sound-speed-water-d_598.html
http://www.ndt-ed.org/EducationResources/HighSchool/Sound/tempandspeed.htm

 

[Raiden2012]

Hmm, I never thought about the temperature part. Was thinking more in terms of density. If the answer is wrong, at least it makes sense. Speed decreases because of increased density and lower temperature.

Wonder if there are any cases where the temperature and density act in opposite directions? Impossible right haha

 

[Ansar]

Thanks. Btw what do the korean words in your sig mean? Something to do with curry?

Where there is a will (뜻이 있는 곳&#50640😉 there is a way (길이 있&#45796😉

Curry in Korean is 카레 (kare)

Wonder if there are any cases where the temperature and density act in opposite directions? Impossible right haha

Well, there are superfluids (such as superfluid Helium-4: http://en.wikipedia.org/wiki/Superfluid)
Below a certain temperature threshold, the fluid loses all viscosity (which is proportional to density, at least kinematic viscosity), so there's that 😉

EDIT: I haven't studied for the MCAT, but I'd put money that you would never encounter superfluids on that exam...that's quantum stuff! 😎

 

[Jepstein30]

Want to clarify here, because now I'm confused.

Among different medium- Speed of sound increases as medium gets more dense (is sound not fastest in solids? molecules closer to eachother..)

Among same medium- Speed of sound increases with increasing temperature (faster vibration)

 

[Raiden2012]

Where there is a will (뜻이 있는 곳&#50640😉 there is a way (길이 있&#45796😉

Curry in Korean is 카레 (kare)

Well, there are superfluids (such as superfluid Helium-4: http://en.wikipedia.org/wiki/Superfluid)
Below a certain temperature threshold, the fluid loses all viscosity (which is proportional to density, at least kinematic viscosity), so there's that 😉

EDIT: I haven't studied for the MCAT, but I'd put money that you would never encounter superfluids on that exam...that's quantum stuff! 😎

Haha oops, I misread the 2nd half of the last sentence. I thought I read (gari eed da) when it was actually (gee ree) Interesting language though

 

[Ansar]

Want to clarify here, because now I'm confused.

Among different medium- Speed of sound increases as medium gets more dense (is sound not fastest in solids? molecules closer to eachother..)

From the website:
The situation with solids is considerably more complicated, with different wave speeds in different directions, in different kinds of geometries, and differences between transverse and longitudinal waves.

So keep in mind things can be a bit more complicated in solids, but this table should give you a general idea of things. : )
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/soundv.html#c1

Did that help?

 

[Charles Darwin]

From the website:
The situation with solids is considerably more complicated, with different wave speeds in different directions, in different kinds of geometries, and differences between transverse and longitudinal waves.

So keep in mind things can be a bit more complicated in solids, but this table should give you a general idea of things. : )
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/soundv.html#c1

Did that help?

v = sqrt(B/rho) ; v = velocity, B = bulk modulus, rho = density

Velocity decreases by the squareroot of the density.

 

[ofi2016]

why does the frequency stay constant in this? the original question is
A pinging device, producing sound at 300 Hz, is submerged in 30°C water. As the water is cooled to 4°C water (the temperature at which water is the most dense):

Answer:
the speed of the sound will decrease and frequency will remain constant.


How do you know the frequency is constant?

 

[gettheleadout]

why does the frequency stay constant in this? the original question is
A pinging device, producing sound at 300 Hz, is submerged in 30°C water. As the water is cooled to 4°C water (the temperature at which water is the most dense):

Answer:
the speed of the sound will decrease and frequency will remain constant.


How do you know the frequency is constant?

Frequency is a source-dependent property of waves, it is invariant throughout propagation even across medium interfaces.