# Sound

• Sound is a mechanical wave - it propogates (moves along) by using the vibrations of particles in matter (as opposed to electromagnetic waves that don't use particles in their propogation!).
• The sound energy is transferred through matter by vibrations of particles in that matter in a longitudinal wave. The vibrations made in a sound wave are parallel to the direction in which the energy is travelling.

• Wavelength (symbol - lamda a Greek letter 'l') is the shortest distance between two corresponding parts of the waveform. For a soundwave that means the shortest distance between two particles of the medium the sound is travelling in that are oscillating in phase. (Shortest distance between two particles that are moving in step with each other). It is measured in metres (m)
• Period (T) is the time taken for one complete oscillation of a particle in the wave. It is measured in seconds (s).
• Amplitude (A) is the maximum displacement from the mean position.
• Frequency (f) is the number of oscillations per second. It cannot be read directly off a graph. You need to find (T) from the displacement/time graph and then find its reciprocal (f =1/T)

In an examination you may be expected to:

I would prefer you to think of the density of air molecules being altered as sound travels through the air rather than you thinking individual molecules get stretched and squeezed...  this video has some good bits and some not so good... see if you can spot them all!

See the waves section for details on wave terms.

Corn starch is a 'shear thickening non-Newtonian fluid' meaning that it becomes more viscous when it is disturbed.

When it's hit repeatedly by something like a speaker cone it forms weird tendrils.

The video below was shot at 30 fps and the speaker cone was vibrating at 30 Hz which is why there is no blur.

This is the original video with the actual sound of the speaker.

The following site covers sound really well - take a look at it.