Jump to content

Two meteorites and sound waves


Recommended Posts

Suppose there are two meteorites which approach the atmosphere of the Earth from different ( maybe opposing) directions.

 

Let us assume that the atmosphere is at rest with respect to an observer at ground level.

At the moment that the two meteorites are in very close proximity to each other, they explode  in a symmetrical way and create sound waves (that do not interfere with each other)

My question is "Does the observer hear  the two explosions at the same time,albeit at different pitches?"

(I am asking this qustion in order to hopefully better understand the invariance of the speed of light , but first I need to understand this present situation)

Link to post
Share on other sites
Posted (edited)
27 minutes ago, mathematic said:

It will depend on where the observer is relative to the meteorites.  Speed of sound is not subject to Lorentz transformation.

So the observer might not hear the two sounds at the same time?

Even though the two sounds emanated from practically the same point in time and space?

Edited by geordief
Link to post
Share on other sites

Your ears can 'locate' the origin of sounds because the sound has to travel different paths to your two ears.
Unless you are V van Gogh, I would think this is apparent.

Link to post
Share on other sites
3 minutes ago, MigL said:

Your ears can 'locate' the origin of sounds because the sound has to travel different paths to your two ears.
Unless you are V van Gogh, I would think this is apparent.

Sorry ,I don't get what you are saying.Suppose the observer is 10 miles from the location in the atmosphere where the two meteorites simultaneously  exploded(or caused sound waves) will the observer hear two explosions at the same time  or will there be a difference in the arrival times of the respective sound waves  on account of the respective states of motions of the two meteorites?

Will the  sound  waves coming  from the meteorite that is ,say mostly moving towards the observer  arrive at the same time as those coming from the other meteorite that is  ,say mostly  moving away from the observer?

 

(I feel they should  both arrive almost simultaneously but it is the first time I have asked myself this question.)

 

Link to post
Share on other sites

What do you mean by 'two' explosions ?

There is only one explosion resulting from their collision, and because your ears are 8 in. apart, you will be able to discern the direction it is coming from.

If there are two explosions resulting from reasons other than a collision ( ?? ), then the explosions are spatially separated, and will arrive at your ears at different times.

These are common, every day occurrences, and readily apparent.
Either that, or I'm totally misunderstanding the question.

Link to post
Share on other sites
53 minutes ago, MigL said:

What do you mean by 'two' explosions ?

There is only one explosion resulting from their collision, and because your ears are 8 in. apart, you will be able to discern the direction it is coming from.

If there are two explosions resulting from reasons other than a collision ( ?? ), then the explosions are spatially separated, and will arrive at your ears at different times.

These are common, every day occurrences, and readily apparent.
Either that, or I'm totally misunderstanding the question.

They explode (or just make sounds waves) separately but at more or less the same location in space and time.

I suppose they are far enough away from each other that their respective sound waves don't interfere too much and the observer makes out two separate sounds coming from the two meteorites (or other objects disturbing the atmosphere,which could be of course any medium)

 

These two events are as close together as practically possible.

 

I want to satisfy  my own mind that the  direction of the meteorites'  trajectory has no bearing on the length of time that it takes the sound wave to reach the observer on the ground.

 

I feel it is just the spatial distance between either of the meteorites and the observer (and of course the medium,) that determines the time taken for the sound wave to travel

 

The medium is taken ,ideally to be at rest wrt  the observer.

Link to post
Share on other sites
13 hours ago, geordief said:

I want to satisfy  my own mind that the  direction of the meteorites'  trajectory has no bearing on the length of time that it takes the sound wave to reach the observer on the ground.

Any disturbance in the atmosphere  will propagate at the speed of sound.
If the disturbance is moving towards/away from you, there will be Doppler effects.
If the disturbance is moving towards you faster than the speed of sound, you will not hear it until the leading shock and disturbance arrives.

Your question, as it is, seems to be 'ill posed', and I don't see what conclusions/insights you can draw from it.
( at least, pertaining to Relativity, which is your usual area of interest )

Link to post
Share on other sites
1 hour ago, MigL said:

Any disturbance in the atmosphere  will propagate at the speed of sound.
If the disturbance is moving towards/away from you, there will be Doppler effects.
If the disturbance is moving towards you faster than the speed of sound, you will not hear it until the leading shock and disturbance arrives.

Your question, as it is, seems to be 'ill posed', and I don't see what conclusions/insights you can draw from it.
( at least, pertaining to Relativity, which is your usual area of interest )

Sure  I did have  a possible connection to relativity on my mind.

 

Let me gather my thoughts  for a few hours or a day and see if I can take it any  further or if this has no bearing on the invariance of the speed of light(where I was going to  and hopefully may still)

Link to post
Share on other sites
22 hours ago, geordief said:

At the moment that the two meteorites are in very close proximity to each other, they explode  in a symmetrical way and create sound waves (that do not interfere with each other)

Meteorites survive passage through the atmosphere, so perhaps you intend 'audible fireballs'.

Even so, these propagate, initially at least, as supersonic bow shocks (sudden pressure discontinuities) rather than sound waves - at velocities dependent on their initial trajectories, and independent (for a while at least) of atmospheric properties.

23 hours ago, geordief said:

My question is "Does the observer hear  the two explosions at the same time,albeit at different pitches?"

If one bolide were travelling towards the observer, and one away, they would be experienced as two blast wave fronts, the first perhaps considerably more powerful than the second. 'Pitch' is meaningless here. There may be some reflected aftershocks, but not necessarily in any ordered sequence.

 

Perhaps your enquiries would be better served with a simpler less energetic case, such as two locomotives in still air, sounding their steam whistles as they passed each other in opposing directions.

In the absence of relatavistic effects, and if the locomotives were perfectly streamlined (ie they weren't dragging a large envelope of air with them) an observer on the station platform would hear two perfectly simultaneous sounds pitched according to their respective Doppler shifts.     

 

Link to post
Share on other sites
32 minutes ago, sethoflagos said:

Meteorites survive passage through the atmosphere, so perhaps you intend 'audible fireballs'.

Even so, these propagate, initially at least, as supersonic bow shocks (sudden pressure discontinuities) rather than sound waves - at velocities dependent on their initial trajectories, and independent (for a while at least) of atmospheric properties.

If one bolide were travelling towards the observer, and one away, they would be experienced as two blast wave fronts, the first perhaps considerably more powerful than the second. 'Pitch' is meaningless here. There may be some reflected aftershocks, but not necessarily in any ordered sequence.

 

Perhaps your enquiries would be better served with a simpler less energetic case, such as two locomotives in still air, sounding their steam whistles as they passed each other in opposing directions.

In the absence of relatavistic effects, and if the locomotives were perfectly streamlined (ie they weren't dragging a large envelope of air with them) an observer on the station platform would hear two perfectly simultaneous sounds pitched according to their respective Doppler shifts.     

 

Thanks,yes I am happy with the two trains scenario.**

It serves my purpose exactly.

 

I am still reflecting on what lesson I can draw from  this result (assuming noone  disagrees with your understanding)

 

** and your information regarding meteorites, fireballs etc.

Link to post
Share on other sites
Posted (edited)
20 hours ago, geordief said:

Sure  I did have  a possible connection to relativity on my mind.

 

Let me gather my thoughts  for a few hours or a day and see if I can take it any  further or if this has no bearing on the invariance of the speed of light(where I was going to  and hopefully may still)

@MigLOK,if I take the two trains scenario of  @sethoflagos  and impose the restriction (if necessary)that the trains travel below the speed of light as well as specifying that the medium is at rest with respect to itself can I say that the speed of sound is "invariant" in the same sense that ,in a vacuum the speed of light is "invariant"?

Or are there still differences between the two situations such that I cannot say this?

It seems to me that ,under my (if necessary) restrictions that sound  waves have a constant speed dependent on the particular (homogeneous and at rest with itself) medium  and  also that this speed is independent of the frame of reference

 

Perhaps I am wrong on this last point?

 

I realize that my restrictions  may make this assertion  of trivial importance but am I correct to describe the speed of sound as invariant under those limited conditions?

Edited by geordief
Link to post
Share on other sites
Posted (edited)
1 hour ago, geordief said:

impose the restriction (if necessary)that the trains travel below the speed of light

(bold by me) 

Yes, it is necessary for the trains to travel below the speed of light :-). I assume you mean the speed of sound?

 

Edited by Ghideon
Link to post
Share on other sites
13 minutes ago, Ghideon said:

(bold by me) 

Yes, it is necessary for the trains to travel below the speed of light :-). I assume you mean the speed of sound?

 

Ah yes,  a scrivener's error 😒

Link to post
Share on other sites
10 hours ago, geordief said:

... as well as specifying that the medium is at rest with respect to itself can I say that the speed of sound is "invariant" in the same sense

In what circumstance would a medium be not at rest with respect to itself?

Perhaps you intended "... at rest with respect to the observer", ie. a restatement of our 'still air' constraint.

Could another restatement of this constraint be that observer and medium must be in the same Galilean reference frame?

If so, then if the constraint was a necessary precondition, wouldn't this imply that the apparent speed of sound was not invariant under a Galilean transformation? 

I stress the word 'apparent' to distinguish between transmission over a measured distance in a measured time interval, as distinct from a physical property of the medium itself. These are two different quantities. Whether the latter is invariant to Galilean transformation is a moot point. 

 

Link to post
Share on other sites
19 minutes ago, sethoflagos said:

Perhaps you intended "... at rest with respect to the observer", ie. a restatement of our 'still air' constraint.

Yes,that is what I meant.Suppose that there were eddies  in the medium(caused by local areas of pressure differences,I think) then that would alter the characteristics of the medium and the speed of sound in it..

 

24 minutes ago, sethoflagos said:

 

If so, then if the constraint was a necessary precondition, wouldn't this imply that the apparent speed of sound was not invariant under a Galilean transformation? 

I stress the word 'apparent' to distinguish between transmission over a measured distance in a measured time interval, as distinct from a physical property of the medium itself. These are two different quantities. Whether the latter is invariant to Galilean transformation is a moot point.

I am finding it a bit hard to follow now .I am probably going to need a longer period of reflection and study  if I am going to make sense of it.

Thanks for your help.I hope I wasn't too confusing.

 

Link to post
Share on other sites
22 minutes ago, geordief said:

Yes,that is what I meant.Suppose that there were eddies  in the medium(caused by local areas of pressure differences,I think) then that would alter the characteristics of the medium and the speed of sound in it.

Nearly. But it isn't the properties of the medium that are changing: it is whether or not the medium is flowing away from you toward the trains, which would delay your detection of the whistles; or flowing toward you from the trains, which would advance the detection. 

If you had no information on airspeed, say for instance you were observing via a remote video camera and microphone, your measurements of the (apparent) speed of sound would vary according to wind speed and direction wouldn't they? 

This is an example of Galilean non-invariance.

Now substitute 'speed of light' & 'luminiferous aether' for 'speed of sound' & 'air'. What happened when Mickleson & Morley tried looking for these telltale Galilean non-invariances in their measurements of the speed of light through the medium of the luminiferous aether? They found none!

This is why there is a fundamental difference between the non-invariant measured speed of sound in air and the invariant measured speed of light in vacuum. 

1 hour ago, geordief said:

Thanks for your help.I hope I wasn't too confusing.

No worries. We've all had to work our way through this some time or other.

 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.