Beats and sound waves

On Tuesday we stoppped for a bit and reviewed any problems/issues/ equations/terms that people were willing to ask about.
Then we discussed "beats". We listened to two tuning forks that were slightly different in their frequencies. This caused the sound waves to reach our ears in such a way that occasionally they cancelled each other out, and other times they combined to a loud sound. The "wa-wa" sound of interference is known as the "beat" and the "beat frequency" is the number of "wa's" per second. This frequency ought to exactly match the frequency difference between the two forks.
If the image isn't moving, click here to see it animated.
Learn more about the "beat" phenomenon here

Then we looked at some more resonance stuff with the mechanical oscillator. We looked at metal sticks that would only resonate at specific frequencies. This is like a swing that will only swing back-and-forth at a certain rate. The shorter the rope, the more rapid will be the natural "resonance" frequency of its oscillation.
We also examined a metal hoop on the oscillator. When this hoop was vibrated from one end, the waves traveled both directions around the hoop. At just the right frequency, we got a standing wave pattern. This looked like the string resonator, but was wrapped around in a circle. The higher the frequency of oscillation, the more nodes/antinodes we would get on the hoop. This is actually a way of understanding the Bohr model of the atom that most of you learned about last year. Only certain conditions will allow for a stable resonance, and similarly in the Bohr atom, only certain orbits are stable, because electrons travel like waves around the nucleus. See photos here