Smartphone-Experiment: Speed of Sound (en)

With two smartphones you can easily determine the speed of sound.

You can also watch a German version of this video:

[lllazarrr]

I'd like to share some of my classroom experiences for this particular experiment, because the students come up with some interesting variations on their own.

They had some difficulties grasping if they should add or subtract the time differences from the start and finish claps. So they wanted to eliminate the time difference for the final clap. One way they achieved this was to clap halfway between the phones (in the middle of the distance). The other approach they used is actually moving the second phone to the same physical location as the first phone, so the final clap was again simultaneous.

Finally, after testing their own ideas, I presented the method given in this video. In all three cases we got the same result. I like that the experiment is simple to perform, yet fun and robust to allow for different creative approaches. Personally, I loved the students ideas so mush, because they are not something I would come up with.

Thanks for the great app! Cheers!

[whoafr]

Une pensée pour ceux qui sont en physique

[JesseMason]

I really hope you got some sort of degree in exchange for gifting the world's physics teachers such a marvelous app.

[jean-francoisb.]

super interesting app ! for the speed of sound, you can also separate the two mobiles by a known distance, clap close to one of them, then gather the 2 mobiles at the same place and clap again, you'll won't have twice the delay.

[michaelsikes]

Hi! Thank you for this app- my son is using it for at-home Physics experiments. His readings gave very consistent calculations for speed of sound when completed outside at 3 different distances. However, our calculation shows V= 358.6. m/sec We see that in dry air at 20C, it would be about 343m/sec. We used an online calculator to try and account for temperature (10C), relative humidity (45%) and air pressure- but this corrected the speed of sound to 337.7. What other variables might be accounting for this discrepancy between our experimentally determined calculation and the one we see online?

[robertocastillo]

Like si vienes por el proyecto de física 2 en cuarentena :)

[benjamin.schreiber]

Die App finde ich genial und dieses Experiment ist ziemlich clever! 👏
Ich nehme an, daß man das vielen Jugendlichen so erklären kann, daß sie es kapieren! 👍
Man kann es ja in einzelne Schritte aufdröseln, damit alle kapieren was wann passiert! 👌
Und wenn das Prinzip allen klar ist, dann sollte die Mathematik für die Auswertung auch nachvollziehbar sein! 🙂

[David-ojlq]

This app is so coool. It’s great!!! Love it. Downloaded it for a speed of sound experiment and I love all the features it has. God bless yall!!!

[janitonttila]

Thank you what a app. I love fysiikka. So I love this.

[nightghost_]

What was the speed u measured?
I cant hear it in video...

[ahindramanna]

Can I use one smartphone in a room for this experiment?🙏🙏🙏

[TforThought]

Ingenious app and people who developed it

[ghayathrijayapalan]

It is an amazing But I would like to what is the range for the acoustic stopwatch?

[guinja]

Phyphox c'est cool





Fifa c'est mieux

[yobabyyo]

This is a great app but this experiment doesn't work well, unfortunately. I've done it several time with my classes already, and the problem is that most phones can't record the times consistently at the precision needed. The result is that you end up with speeds of sound anywhere from half to twice the correct value. To be fair: I didn't try yet outside, so maybe that would work better (fewer echoes in the hallways!). I'll add a comment in case it works better outside (or not).

[donhimbeault]

I wonder if this can be used to measure the speed of "sound" in a solid medium, like say a pipe? perhaps by using a microphone in contact with the surface, and tapping the object? Or would reflections be too much interference. That would make a nice demo of how the speed changes for different mediums.

[LouisWongPhysics]

This won't work well because the distance is too short and it also involves reaction time...the uncertainty is too high

[matthieuc]

Great experiment, but i have a question. To what would you connect this experiment to in a real life situation? Like, after doing the experiment what do we get out of it? Thanks.