Determine the Speed of Sound

I will go through a process that will allow you to determine the speed sound travels. This is a classic physics lab that in the past would have required lots of expensive equipment. The only expensive equipment involved here is a computer with a microphone input. Which by itself can be expensive, but most classrooms these days have at least one in the room.

Step 1: Stuff You Need

1. Computer with microphone input
2. Microphone you can plug into the computer
3. Long tube. I typically use discarded carpet tube (which is free), but you can use PVC pipe. 1.5 m to 2 m in length is best.
4. An audio recording program. I recommend Audacity. [http://audacity.sourceforge.net/]

Comments

[llanyort]

question(s) - 1)what if you wanted to measure the distance from the object(that created the sound) to the microphone that captured the sound ? 2)what if you placed two or three other microphones in the room in each corner, could you use them as well ? or would they cause any foreseeable problems in this project ? Im trying to pinpoint the distance and vector of an orignating sound. Is this possible ?

[falconphysics]

I've not tried using multiple microphones with Audacity before. I'm not sure you could do that. What you could do would be to wire two mono microphones to the stereo input and record as a stereo track though.

[llanyort]

thats a good idea !!! thanks.. :-)

[MAD LAB]

i am still a student taking up bs physics!! just want to ask wer can f find audacity program in our computer system! pls help me tanx

[cowgomoo]

well i dont know what the hell you just asked but if i get what your saying, no audacity does not come standard on your computer. google "audacity download" and it should take you to the audacity homepage. just download the version that your system requirements meet.

[Kiteman]

Why do people assume you need high-tech equipment to do decent science? You can calculate the speed of sound with two lumps of wood, a stopwatch and a convenient wall.

[ewilhelm]

How long do you think you can get away with having a comment like this and no Instructable showing us how?

[Kiteman]

Doh! OK, I know what I'm doing with my Science Clubbers tomorrow night...

[falconphysics]

You're right, you don't need high-tech equipment to do decent science. In many cases I do very low tech labs. It all depends on what I'm trying to teach. The tech tools can often be more engaging for students, which is one of the reasons I use them. Additionally we use Audacity for some later labs and this provides a great introduction to the program.

[mrmath]

Makes me wonder two things. 1) Is there anything open source can't do? :) 2) How'd they do it before the computer made it this darn easy?

[Mister_Caipirinha]

2) answer: Two microphones one meter apart connected to an oscilloscope. Do I get another prize??

[falconphysics]

Sure, if I win the laser cutter I'll send you not one, but two official prizes. ;)

[Mister_Caipirinha]

It is also worth pointing out that the pulse comes back inverted - that first "down" peak comes back as an "up" peak - since the end of the air tube can be considered as fixed (cement has larger impedance than the air). If you can detect a reflection from the end just held up in the air it may be erect (assuming air not surrounded by the tube has a lower impedance that air in the tube). Neat!

[falconphysics]

Give the man a prize. The wave is indeed inverted when it reflects.