Speed of Sound

[DocDrakeRamoray]

What increases speed of sound? ( in the medium)

If I increase wavelength of a sound wave, will speed of the wave increase?

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[Bernoull]

What increases speed of sound? ( in the medium)

If I increase wavelength of a sound wave, will speed of the wave increase?

For a given medium, wavelength and frequency are inversely proportional and their product equals the wave velocity. For the MCAT, wave velocity is constant for a given medium therefore if you increase wavelength, frequency necessarily must decrease and viceversa. Think of it like k=wf. k=constant=velocity; w=wavelength and f=frequency.

Keep in mind that, for gas media, temperature affects sound velocity where higher temperature = higher velocity.and viceversa.

I answered a similar question b4 on sound velocity, here's the link
http://forums.studentdoctor.net/showthread.php?t=613286

Hope this helps.

 

[0Complications]

For a given medium, wavelength and frequency are inversely proportional and their product equals the wave velocity. For the MCAT, wave velocity is constant for a given medium therefore if you increase wavelength, frequency necessarily must decrease and viceversa. Think of it like k=wf. k=constant=velocity; w=wavelength and f=frequency.

Keep in mind that, for gas media, temperature affects sound velocity where higher temperature = higher velocity.and viceversa.

I answered a similar question b4 on sound velocity, here's the link
http://forums.studentdoctor.net/showthread.php?t=613286

Hope this helps.

So do the size of gas particles in the medium. Larger particles = lower velocity; smaller particles = higher velocity.

eg. Velocity of sound in H2 (g) at 30 degrees C > Velocity of sound in O2 (g) at 30 degrees C.

 

[Bernoull]

So do the size of gas particles in the medium. Larger particles = lower velocity; smaller particles = higher velocity.

eg. Velocity of sound in H2 (g) at 30 degrees C > Velocity of sound in O2 (g) at 30 degrees C.

By size are do u mean density? Sound velocity is determined by

v = sqrt(B/p) where B=bulk modulus (measure of stiffness) and p = density.

I dont see how size by itself changes velocity. Bear in mind H2 is < dense than O2 therefore sounds travels faster in H2. I thinking ur conflating size and density.

 

[0Complications]

By size are do u mean density? Sound velocity is determined by

v = sqrt(B/p) where B=bulk modulus (measure of stiffness) and p = density.

I dont see how size by itself changes velocity. Bear in mind H2 is < dense than O2 therefore sounds travels faster in H2. I thinking ur conflating size and density.

Good call. You are right. It is density not size.

 

[vickpick]

and yea... increasiong lambda increase velocity.. v=lambda f...

 

[Bernoull]

and yea... increasiong lambda increase velocity.. v=lambda f...

where did u read that??

 

[vickpick]

lol ...light is a wave so wavelength times freqency (m*s^(-1))=m/s or v..
so if lambda increase velocity increases.. lambda is the notation for wavelength (i'm sure u knew that.. )

 

[vickpick]

umm.. and where did I read that... probably in my 10th grade AP chem class... and then again in 12th grade AP physics... haven't taken inorgo chem or physics in college yet.. but im pretty sure im right..

as for the medium.. the thinner the medium - the light travels.. i think notation for the measure os the thickness or thinness of medium is "n"... has been a long time though.. so i can be wrong on the correct notation..

 

[Bernoull]

lol ...light is a wave so wavelength times freqency (m*s^(-1))=m/s or v..
so if lambda increase velocity increases.. lambda is the notation for wavelength (i'm sure u knew that.. )

From, ur AP classes, wat happens to freq when wavelength increases????

 

[Bernoull]

umm.. and where did I read that... probably in my 10th grade AP chem class... and then again in 12th grade AP physics... haven't taken inorgo chem or physics in college yet.. but im pretty sure im right..

as for the medium.. the thinner the medium - the light travels.. i think notation for the measure os the thickness or thinness of medium is "n"... has been a long time though.. so i can be wrong on the correct notation..

lol ...light is a wave so wavelength times freqency (m*s^(-1))=m/s or v..
so if lambda increase velocity increases.. lambda is the notation for wavelength (i'm sure u knew that.. )


Both ur certitude and confidence are misplaced.

The original question asked how to increase the speed of sound, which is a mechanical wave. You talk about light which has dual nature, but it's wave properties result from electromagnetic phenomena, not mechanical so there are important differences. Anyway I'll use a light example to clarify things

Now if your assertion that increase &#955; increases velocity is true, when light's &#955; is increased in a vacuum, its velocity should exceed c (3E8m/s) which is impossible with today's physics!!

Electromagnetic properties of light including velocity can be derived from maxwell's equations (2nd ODE solutions of Maxwell's 3rd n 4th equations) and c=E/B where E and B are the magnitudes of the electric field and magnetic fields respectively. Although numerically E is ~ 3E8 times larger than B, their units are different and their values are equal.

yes, yes everyone knows of v=&#955;f and it usually gets people in trouble. It's mathematically simply but without understanding of some concepts it is HIGHLY misleading, hence this discussion. One needs to appreciate both the utility and limitation of this equation. It tells u nothing about what properties of a medium affect wave velocity.


Once again, mechanical wave velocity is in almost all cases is determined by the MEDIUM. Two properties of the medium determine velocity.
1. Elastic component: speeds up waves
2. Inertial component: slows waves down

(if medium is gas, sound velocity increases with temperature also)

For sound wave, v = sqrt(B/p) where B=bulk modulus (measure of stiffness) and p = density.

For wave on a string, v = sqrt(T/ &#956; ) where T= tension and &#956; = linear mass density.
Surface waves (nondispersive medium) v=sqrt(gy) where g=acceleration due to gravity and y is depth of liquid. Eq valid only where y is much less than wave &#955;.
Surface waves (dispersive medium) v=sqrt(g&#955;/(2pi)) where g=acceleration due to gravity .

 

[vickpick]

lol ...light is a wave so wavelength times freqency (m*s^(-1))=m/s or v..
so if lambda increase velocity increases.. lambda is the notation for wavelength (i'm sure u knew that.. )


Both ur certitude and confidence are misplaced.

The original question asked how to increase the speed of sound, which is a mechanical wave. You talk about light which has dual nature, but it's wave properties result from electromagnetic phenomena, not mechanical so there are important differences. Anyway I'll use a light example to clarify things

Now if your assertion that increase &#955; increases velocity is true, when light's &#955; is increased in a vacuum, its velocity should exceed c (3E8m/s) which is impossible with today's physics!!

Electromagnetic properties of light including velocity can be derived from maxwell's equations (2nd ODE solutions of Maxwell's 3rd n 4th equations) and c=E/B where E and B are the magnitudes of the electric field and magnetic fields respectively. Although numerically E is ~ 3E8 times larger than B, their units are different and their values are equal.

yes, yes everyone knows of v=&#955;f and it usually gets people in trouble. It's mathematically simply but without understanding of some concepts it is HIGHLY misleading, hence this discussion. One needs to appreciate both the utility and limitation of this equation. It tells u nothing about what properties of a medium affect wave velocity.


Once again, mechanical wave velocity is in almost all cases is determined by the MEDIUM. Two properties of the medium determine velocity.
1. Elastic component: speeds up waves
2. Inertial component: slows waves down

(if medium is gas, sound velocity increases with temperature also)

For sound wave, v = sqrt(B/p) where B=bulk modulus (measure of stiffness) and p = density.

For wave on a string, v = sqrt(T/ &#956; ) where T= tension and &#956; = linear mass density.
Surface waves (nondispersive medium) v=sqrt(gy) where g=acceleration due to gravity and y is depth of liquid. Eq valid only where y is much less than wave &#955;.
Surface waves (dispersive medium) v=sqrt(g&#955;/(2pi)) where g=acceleration due to gravity .

ummm.... read the actual questions.. there were two of them.. first what in a medium changes speed... and then the second q asking.. does increasing wavelength increase the velocity?

i answered the second question..the questioner didn't really mention other conditions so y make a simple question difficult... i didn't comment on the first one... but u clearly have more understanding of physics than I do.. so ok, u're right... i retreat

in here I used light as its the most known example of wave..

in a change of medium the E remains the same therefore the frequency remains the same.

 

[vickpick]

From, ur AP classes, wat happens to freq when wavelength increases????

in a change of medium the E remains the same therefore the frequency remains the same.

 

[Bernoull]

umm.. and where did I read that... probably in my 10th grade AP chem class... and then again in 12th grade AP physics... haven't taken inorgo chem or physics in college yet.. but im pretty sure im right..

as for the medium.. the thinner the medium - the light travels.. i think notation for the measure os the thickness or thinness of medium is "n"... has been a long time though.. so i can be wrong on the correct notation..

I should have picked up that u were thinking about light wave travelling in different media (opposed to within a given medium), from ur reference to n (refractive index). Clearly light speed changes then because the medium changed n=c/v. In this case ur absolutely right, freq is constant and velocity changes with wavelength.

 

[rocketbooster]

You guys are confusing a lot of things together. Let's make it simple shall we?

Light:

Velocity in Different Media: vacuum>gas>liquid>solid
why? because the less dense the medium, the faster the light travels. within each medium, frequency is constant, and velocity and wavelength are variable.
why? n=c/v=c/(lambda*f). Greater refractive index means more dense of a medium, so the denominator decreases as n increases.

Sound:

Velocity in Different Media: solid>liquid>gas>vacuum (actually v=0 in vacuum because sound travels through vibrations in the medium, and there are no molecules in a vacuum)
why? sound is a mechanical wave and travels through the vibrations of the medium's molecules. the speed of sound=((restoring force or molecular kinetic energy)/molecular inertia). the most important part of the equation is really the restoring force when comparing solid vs liquid vs gas. the faster the wavelength transmits from one molecule and returns to the original (restoring force), the faster the next wave of sound can be sent out. so, with solids, the molecules are closer together, so it's less distance for the restoring force to travel.


Someone started bringing up how to determine the speed of a gas. That only applies if you're in a gaseous medium. Generally, speed of sound questions test to see if you know how speed changes in different medium between solid, liquids, gases, or a vacuum. However, you should note that the rules for the speed of gas molecules are actually quite similar to speed of sound in different media.

Speed of gas = (T/m)^1/2
Speed of sound = ((Restoring force or molecular kinetic energy)/(molecular inertia))^1/2

If you increase T, molecular kinetic energy goes up. Molecular inertia can be thought of mass density. So, they are definitely similar relationships BUT not identical. The speed of a gas has nothing to do with restoring force and only inversely relates to mass, not mass density.

 

[Fifty 3rds]

I thought increased density led to increased velocity. With increased density, molecules are packed more tightly allowing the vibrations of sound to be passed from one molecule to the next more quickly. That is why sounds travels faster in water than in air, right?

 

[rocketbooster]

I thought increased density led to increased velocity. With increased density, molecules are packed more tightly allowing the vibrations of sound to be passed from one molecule to the next more quickly. That is why sounds travels faster in water than in air, right?

My fault, I meant "mass density" is molecular inertia. I just corrected it. Mass density is different than density. Mass density=m/L, where m=mass and L=length of the linear x-coordinate along the mass.

So, think about it, if the mass per unit length is greater, then the sound wave takes longer to send through because its going through a greater mass.