Sound waves versus equilibrium

Click For Summary
SUMMARY

The discussion centers on whether a parcel of air transmitting sound waves can be considered in a state of equilibrium. Participants argue that according to kinetic gas theory, a gas is in equilibrium when its entropy is maximized. However, they conclude that a gas transmitting sound waves does not meet this criterion, as it is not an isolated system with constant internal energy and volume. Therefore, the Ideal Gas Equation of State at Equilibrium does not apply to such a parcel of air.

PREREQUISITES
  • Kinetic Gas Theory
  • Thermodynamic Equilibrium
  • Entropy Maximization
  • Ideal Gas Equation of State
NEXT STEPS
  • Study the principles of Kinetic Gas Theory in detail
  • Explore the concept of thermodynamic equilibrium and its implications
  • Research the relationship between entropy and isolated systems
  • Examine the Ideal Gas Law and its limitations in non-isolated systems
USEFUL FOR

Physicists, thermodynamics students, and anyone interested in the principles of gas behavior and sound wave propagation.

klimatos
Messages
411
Reaction score
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?
 
Physics news on Phys.org
What is your definition of equilibrium?

Match this against the situation and post your answer.
 
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.
 
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?
 
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.
 
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?
 
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?
 
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 :)
 
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!
 

Similar threads

Undergrad Does two-slit sound-wave interference pattern return to original form?
  • · Replies 10 ·
Replies
10
Views
2K
High School Parcel theory -- how can there be buoyancy with miscible gases?
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad A Question About Shock Waves From an Airplane
  • · Replies 82 ·
3
Replies
82
Views
8K
High School What sound frequencies can pass through a hole in a wall?
  • · Replies 31 ·
2
Replies
31
Views
4K
High School Does sound pass through bricks? Can I deflect sound away?
  • · Replies 21 ·
Replies
21
Views
3K
Undergrad Signal Transmission Using Sound Waves
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad What Does a Graph of Sound Wave Pressures in the Atmosphere Reveal?
  • · Replies 9 ·
Replies
9
Views
2K
Graduate Relaxation times of molecules during sound propagation
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad How Does Sound Behavior Change in Low Atmosphere?
  • · Replies 1 ·
Replies
1
Views
8K
Undergrad Amplitudes of longitudinal sound waves
  • · Replies 8 ·
Replies
8
Views
3K