Sound+and+waves


 * Sound and Waves**

(This page will have to be tidied up later but I'm just throwing something together for those of you stuck in a snowdrift.)

Here's the rough order of play for the session: 1. Make a musical instrument. How does it actually make a sound? What makes it louder? What changes the pitch? In terms of the physical model, how do these changes work?

2. Measuring the speed of sound: Using Audacity (free download) and a cheap pair of earphones, clap-and-echo, balloon bursting, dual beam oscilloscope and any other method that you can think of. HSW: considerations of accuracy and reliability. How can we measure the speed of sound in other media?

3. Demonstrations of the nature of sound and waves: Capturing and analysing sound waves with Audacity Slinky! Transverse and longitudinal waves - differences and similarities. What determines wave speed? Using an oscilloscope; signal generators, frequency and hearing response. What is loudness? Sonometers, ripple tanks and other tricksy equipment.

4. Quantitative work: Understanding the v= f l relationship. Period and frequency. Frequency and pitch, musical relationships, phase relationships. Constructive and destructive interference, beats. Tension of a wire and fundamental frequency, music and maths. Timbre.

All of the resources are in this mis-named zip file!

If you're going to use audacity to measure the speed of sound, you have to do it with a computer that has a stereo sound card! You need to be able to assign each side of the sound in to a different channel so that you get a trace from each of the microphones (we were using cheap earphones). More destructions here on Computer Science for Fun. (Yep, I know exactly what you're thinking...) Speaking of Audacity, James started a highly ambitious list called "99 things to do with Audacity" which I include on a new wiki page for your delectation. Let's see if we can get it up to 20?
 * Wisdom painfully acquired on the day**:

Making musical instruments is always fun. It's a good idea to have some information on how traditional musical instruments work or to give students access to sites like 'How stuff works' if you're going to get useful accounts of the physics out them. It's also a good follow up to get one of your electric guitarists to bring in their instrument - you can uncover a speaker, put polystyrene balls in it to show the mechanism for sound propogation, connect the output to a CRO and look at pitch and frequency, amplitude and loudness and rock out to 'Purple Haze'.

The Cathode Ray Oscilloscope is one of those bits of kit that just gives many teachers the willies. It shouldn't - it's basically just a voltmeter with an adjustable sensitivity and a time-base on the x-axis. It's mostly used to look at sound and AC in the lab - teach yourself how it works rather than remembering a list of settings and you'll be fine. Ripple tanks are all well and good but quite a bit of faffing to get an effect that you might well prefer to achieve via pictures of waves at sea and the like (do an image search for 'diffraction sea', for example) so consider the nature of the teaching and learning before you order the kit.

On the other hand, as long as you don't have any photosensitive epileptics in the class, it's always worth getting a strobscope out. Demonstrate 'beating' (steady...) for slightly detuned guitar strings and illustrate the principle with a pair of pendula. Stroboscopic events are surreal and will be sure to impress and raise questions if handled right.