Posted December 19, 2000
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I have lots of music to play today, so I want to get started on it right away before I start talking about ... waves. This is Mozart's piano concerto no. 25 in C, number 503, performed by the academy of st. martin in the fields. What a great name for an orchestra.
You just heard Mozart's piano concerto no. 25 in C, number 503, performed by the academy of st. martin in the fields, from a philips CD which I highly recommend, by the name of "the great piano concertos volume II".
what is a wave? wave has many meanings -- waves goodbye, doing the wave, ocean waves, heat waves, microwaves, airwaves, sound waves -- they all refer to the same concept: a self-perpetuating pattern.
ocean waves. What is an ocean wave made of? water, sort of. But the water molecules don't move along with the wave. The wave is a pattern of rising and falling water. It's not made of anything, per se.
sound waves. When you hear something, your ear is detecting patterns of changing air pressure. Or water pressure, if you're underwater.
microwaves and airwaves are two kinds of electromagnetic radiation, which means that they're patterns of changing magnetic fields.
moving waves have a characteristic speed, which depends on what medium they're travelling through. You might have noticed that ocean waves travel at the same speed, regardless of how tall they are. Electromagnetic waves, like microwaves and light, move through space at 300,000 km/s; sound travels through air at 330 m/s, slightly faster through water.
Which brings us to...
standing waves: Waves that don't move at all.
Standing waves are good examples to study, because they stay in one place long enough for you to get a good hard look.
Consider a grandfather clock. It's a really good example because of the parallel between the characteristic speed of sound, and the characteristic frequency of a pendulum. Sound travels at the same speed regardless of frequency; and a pendulum swings at a steady frequency even as it loses momentum and covers a smaller and smaller distance.
All this talk about waves seems really easy until someone comes along and asks you whether light is just a wave, or whether it's really a very small particle that acts like a wave. Then you use up a few hundred years trying to figure out which one it is, and eventually you decide that it's both. And everything else is both. Apparently, every particle acts like a wave to some extent; and every wave acts like a particle to some extent.