Measuring the Velocity of Sound in this Lab Exercise

[srnixo]

Homework Statement

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Relevant Equations

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Here is the exercise:

Which one seems logical and correct ?​

this one:
[ Normally when we increase distances, the velocity of sound decreases?]

Or this one?

You might wonder why. Well, my friend in class told me that the second table could be correct because the experiment was conducted at closed home under suitable conditions, where the average speed of sound is around 343 and the calculated speed is approximately 333, which is slightly lower than the standard value but still within a reasonable range of deviation so somewhat acceptable within the limits!
and she told me also that in home, when we increase distances, the velocity of sound remains constant. This is because the speed of sound in a medium (such as air) is determined by the properties of that medium, and not by the distance traveled within it.
could you please help me!

 

[berkeman]

[ Normally when we increase distances, the velocity of sound decreases?]

No, of course not. The speed of sound in air depends on the air temperature, pressure, humidity, etc., but certainly not on distance through air with those variables held constant.

 

[berkeman]

The more likely issue is that when you are trying to use a simple measuring apparatus like cell phones, the closer the distance the higher the error...

 

[srnixo]

The more likely issue is that when you are trying to use a simple measuring apparatus like cell phones, the closer the distance the higher the error...

Exactly! I have noticed that even after repeating the experiment several times.

But,
Does that mean that the second table is correct and its explanation is accurate? It is unreasonable for the speed of sound to remain the same even if the distances are changed to farther ones!

 

[berkeman]

But,
Does that mean that the second table is correct and its explanation is accurate? It is unreasonable for the speed of sound to remain the same even if the distances are changed to farther ones!

The speed of sound is not changing with distance in your lab measurements. The accuracy of your measurement apparatus is being compromised by trying to do the measurements at 1m, etc.

 

[srnixo]

The speed of sound is not changing with distance in your lab measurements. The accuracy of your measurement apparatus is being compromised by trying to do the measurements at 1m, etc.

I know that the speed of sound is not directly related to distances but is influenced by external factors such as humidity and temperature. However, in the given exercise, after taking the measurements, you should provide a result and make conclusion from what you notice . In this case, what would you do?

 

[berkeman]

However, in the given exercise, after taking the measurements, you should provide a result and make conclusion from what you notice . In this case, what would you do?

I would figure out what is causing the systematic errors in my measurement apparatus. You?

 

[nasu]

The first value in the second table is wrong. The time interval is 0.006.
The table feels like is made up. The values are too nice. Just that in the first row the author was not careful.

 

[srnixo]

I would figure out what is causing the systematic errors in my measurement apparatus. You?

If that's the case, it's difficult to determine. The experiment was conducted under suitable conditions, with the room's shape allowing sound waves to be straight. Additionally, there was no external influence from temperature, humidity, or even the closure of the room. The sensitivity of the microphones was adjusted before conducting the experiment to avoid noise. Therefore, I don't think this is the final conclusion of the experiment! Hum!?

 

[srnixo]

The table feels like is made up. The values are too nice. Just that in the first row the author was not careful.

Oh! which one? the first table or the second one!

 

[nasu]

The second one, as I said.

 

[berkeman]

If that's the case, it's difficult to determine. The experiment was conducted under suitable conditions, with the room's shape allowing sound waves to be straight. Additionally, there was no external influence from temperature, humidity, or even the closure of the room. The sensitivity of the microphones was adjusted before conducting the experiment to avoid noise. Therefore, I don't think this is the final conclusion of the experiment! Hum!?

It would help if you posted a diagram of the experiment along with the procedure for the experiment. It looks like there may be a link in your OP, but it does not seem to be separately clickable for me, and I'm not inclined to do a bunch of extra work to try to figure this out. Post a diagram of the setup, and give us your thoughts on where the systematic errors may be coming from.

After all, you have not discovered an amazing anomaly that has never ever been seen before (the variation of the speed of sound with distance). You have discovered that there is a problem with this experimental setup. Figure that out please.

 

[srnixo]

The second one, as I said.

Alright. Mr @nasu , not just for the homework , but for my general knowledge as a student of physics, is it true that the speed of sound in enclosed spaces, like houses or adjacent rooms, remains the same [ as the average speed of sound in dry air at 20 degrees Celsius which is approximately 343 meters per second ]even if the distance between you and the listener increases?

 

[srnixo]

It would help if you posted a diagram of the experiment along with the procedure for the experiment. It looks like there may be a link in your OP, but it does not seem to be separately clickable for me, and I'm not inclined to do a bunch of extra work to try to figure this out. Post a diagram of the setup, and give us your thoughts on where the systematic errors may be coming from.

After all, you have not discovered an amazing anomaly that has never ever been seen before (the variation of the speed of sound with distance). You have discovered that there is a problem with this experimental setup. Figure that out please.

That link doesn't provide any benefit because it only explains how to conduct the experiment, and that is already mentioned at the beginning of the exercise.
Additionally, believe me, I don't know what the conclusion is because, before conducting the experiment, I ensured all necessary conditions to avoid errors and repeated it about five times approximately.
However, if the second table is correct, the conclusion is clear, and I have written it in the explanation, but if it's not then this is the problem , there is nothing to deduce about i guess

 

[haruspex]

Your problem, if you have followed the video exactly, may be that the source of sound is not right at the first phone, but some short distance, y, above it. The difference in the recorded times will be in proportion to the difference in the two travel distances.
If the (horizontal) distance between the phones is x then the two travel distances are $y, \sqrt{x^2+y^2}$, making the difference $\sqrt{x^2+y^2}-y$.
See if using that instead of x gives more consistent results. Certainly it should produce lower speeds for the shorter x values.

 

[srnixo]

Your problem, if you have followed the video exactly, may be that the source of sound is not right at the first phone, but some short distance, y, above it. The difference in the recorded times will be in proportion to the difference in the two travel distances.
If the (horizontal) distance between the phones is x then the two travel distances are $y, \sqrt{x^2+y^2}$, making the difference $\sqrt{x^2+y^2}-y$.
See if using that instead of x gives more consistent results. Certainly it should produce lower speeds for the shorter x values.

I repeated the experiment five times, and obtained the first table. Although I know that the speed of sound is not directly related to distances, but in the exercise, to calculate the speed of sound you need to consider distances because it is Vs=2.D/∆T . I got confused because the second table seems also logical ( velocity of sound is not related to distances so it remains constant).
For that reason, i'm asking which table is correct for this exercise to make things clear.

 

[haruspex]

I repeated the experiment five times, and obtained the first table. Although I know that the speed of sound is not directly related to distances, but in the exercise, to calculate the speed of sound you need to consider distances because it is Vs=2.D/∆T . I got confused because the second table seems also logical ( velocity of sound is not related to distances so it remains constant).
For that reason, i'm asking which table is correct for this exercise to make things clear.

You don't seem to have understood my post. As others have posted, the speed of sound certainly does not vary with distance.

I am saying that the distances you used in the first table are wrong if they are the distances between the phones. The sound is not going from one phone to the other; it is going from the clapped hands to both phones.

You need to figure out how far it was from the clapping hands to the far phone, how far from them to the near phone, subtract the latter from the former, and use that as the distance in the table.

For example, your first distance in the table is 1m. Assuming the hands were 0.4m above the phone then the two distances the sound had to travel were 0.4m and 1.077m. The difference is 0.677m. With the time difference of 0.004s, that gives a speed of 383m/s, a much more reasonable number.

However, making that same assumption at the longer distances only makes the results there worse (slower). To make the speeds about the same for all distances the height of the hands needs to be about 1m, but that makes the speeds only around 220m/s.

 

[nasu]

Alright. Mr @nasu , not just for the homework , but for my general knowledge as a student of physics, is it true that the speed of sound in enclosed spaces, like houses or adjacent rooms, remains the same [ as the average speed of sound in dry air at 20 degrees Celsius which is approximately 343 meters per second ]even if the distance between you and the listener increases?

You are insisting on the fact that you measured in a closed space as this being relevant.
The speed of sound depends only on the conditions of the medium. For sound in air the temperature and humidity are the main parameters that have an effect on the speed of sound.

Now, it is very unlikely that the temperature or humudity varies signifcantly over a few meters but not impossible in principle. But anyway, even if this were the case, it is not the distance that affects the speed but the variation in the conditions of the medium. Actually, indoors may be more likely to have temerature and humidity gradients if you have heaters or (de)humidifiers.

But I doubt that these effects can explain the large variation that you observed. For example, you need to go to about -100 Celsius to decerase the speed to about 260 m/s. The first table cannot be explained by variations in the conditions of the medium, no matter if you did the experiment indoors or outdoors.

It's more likely something to do with the experimetal setup, as sugested by @haruspex.

 

[haruspex]

For sound in air the temperature and humidity are the main parameters that have an effect on the speed of sound.

Just to cover the bases, what about wind? Since the experiment adds the times for the two directions, the net effect of a wind speed of v parallel to those directions would be to cut the measured speed from c to $c-\frac{v^2}c$. Even with a wind speed of 72km/h, that's a reduction of less than 1.2m/s.

 

[srnixo]

I got it now, @nasu , @haruspex , @berkeman Thank you so much for your consideration, and thanks for all these explanations to help me I appreciate it