Sound waves versus equilibrium

In summary, the conversation discusses the concept of equilibrium in relation to a parcel of air transmitting sound waves. The participants debate whether or not the parcel can be considered in a state of equilibrium and what the definition of equilibrium is. The conversation also touches on kinetic gas theory and its assumptions, as well as the concept of an isolated system and its relation to entropy. The conversation ends with a slight tangent about the timing of bringing up a topic in a conversation.
  • #1
klimatos
411
36
Postulate a parcel of air that is transmitting sound waves. Can that parcel ever be considered to be in a state of equilibrium? I maintain that it cannot. How say you?
 
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  • #2
What is your definition of equilibrium?

Match this against the situation and post your answer.
 
  • #3
Studiot said:
What is your definition of equilibrium?

Match this against the situation and post your answer.

Fair enough. Kinetic gas theory says a gas is in a state of equilibrium when its entropy has been maximized. I maintain that a gas transmitting sound waves is not in a state of maximum entropy. Consequently, the Ideal Gas Equation of State at Equilibrium would not apply to that parcel of air.
 
  • #4
Kinetic gas theory says a gas is in a state of equilibrium when its entropy has been maximized.

Not quite.

A system is said to be in equilibrium when it has no further tendency to change its properties of interest.

In particular considering thermodynamic equilibrium (it is not the kinetic theory by the way) a system is isolated if the internal energy and volume are constant.

It can be shown that in an isolated system (with constant U and V) the entropy tends to a maximum.

So yes for an isolated system in equilibrium, the entropy is a maximum

Is your gas an isolated system?
 
  • #5
Kinetic Gas Theory makes a whole range of assumptions which are not completely true. Complete elasticity of collisions is ALMOST completely true, but not quite.
 
  • #6
We would not expect a volume of air with sound waves passing through it to satisfy the OPs definition of being in equilibrium because the volume of air is not an isolated system.
Why would anyone think it might be?

It is not clear what the point of the 1st post is.
If the intention is to start a conversation, as in social media, then isn't it more polite to kick things off yourself?
 
  • #7
Simon Bridge said:
If the intention is to start a conversation, as in social media, then isn't it more polite to kick things off yourself?

I agree. Point taken. But why wait more than two years to bring this to my attention?
 
  • #8
klimatos said:
I agree. Point taken. But why wait more than two years to bring this to my attention?
Because I'm an idiot?

I only just noticed and didn't check the date stamp - it happens :)
 
  • #9
Simon Bridge said:
Because I'm an idiot?

I only just noticed and didn't check the date stamp - it happens :)

No harm, no foul.
 
  • #10
Red Wizard needs coffee - urgently!
 

What are sound waves and how do they differ from equilibrium?

Sound waves are a type of mechanical wave that travel through a medium, such as air or water, by causing particles in the medium to vibrate. Equilibrium, on the other hand, refers to a state where there is no net force or motion in a system. In other words, sound waves are a form of energy that can exist in equilibrium systems, but they are not the same as equilibrium itself.

How do sound waves propagate?

Sound waves propagate through a medium by causing particles in the medium to vibrate back and forth in the direction of the wave's motion. As the particles vibrate, they transfer energy to neighboring particles, creating a chain reaction that allows the wave to travel through the medium.

What factors influence the speed of sound waves?

The speed of sound waves is influenced by the properties of the medium through which they travel. In general, sound waves travel faster through denser materials, such as solids, and slower through less dense materials, such as gases. Temperature can also affect the speed of sound waves, with higher temperatures typically resulting in faster sound waves.

How does the amplitude of a sound wave relate to its intensity?

The amplitude of a sound wave is directly related to its intensity, or loudness. Intensity is a measure of the amount of energy that a sound wave carries per unit of area, and it is directly proportional to the square of the sound wave's amplitude. This means that as the amplitude of a sound wave increases, its intensity also increases.

What is the difference between frequency and wavelength of a sound wave?

Frequency and wavelength are two different properties of sound waves. Frequency refers to the number of complete cycles or vibrations that a sound wave makes in one second, and it is measured in Hertz (Hz). Wavelength, on the other hand, refers to the distance between two consecutive points on a sound wave that are in phase, or vibrating in the same direction at the same time. It is typically measured in meters (m).

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