equilibrium position; this is known as simple harmonic motion. Actually, simple
harmonic motion is an idealization that applies only when friction, finite size, and
other small effects in real physical systems are neglected. But it is a good enough
approximation that it ranks in importance with other special kinds of motion (free
fall, circular, and rotational motion) that you have already studied. Systems that can
be analyzed in terms of simple harmonic oscillations include cars without shock
absorbers, a child's swing, violin strings, and, more importantly, sound waves and
certain electrical circuits that you will study in later lessons.

Week of March 23, 1998 - Spring Break

Week of March 30, 1998
Lesson 11Traveling Waves
Keywords: waves; Types Of Waves; Properties Of Waves;
OBJECTIVES:
* Define and recognize the following:transverse waves, phase velocity,
longitudinal waves, wavelength, wave train, wave number, wave front, traveling
wave.
* Describe, and interpret descriptions of, traveling transverse waves on a string,
using both graphical and mathematical formulations.
Comments: For many people--perhaps for most--the word 'wave' conjures up
a picture of an ocean, with the rollers sweeping onto the beach from the open
sea. If you have stood and watched this phenomenon, you may have felt that for
all its grandeur it contains an element of anticlimax. You see the crests racing in,
you get a sense of the massive assault by the water on the land--and indeed the
waves can do great damage, which means that they are carriers of energy--but yet
when it is all over, when the wave has reared and broken, the water is scarcely
any further up the beach than it was before. That onward rush was not to any
significant extent a bodily motion of the water. The long waves of the open sea
(known as the swell) travel fast and far. Waves reaching the California coast
have been traced to origins in South Pacific storms more than 7000 miles away,
and have traversed this distance at a speed of 40 mph or more. Clearly the sea
itself has not traveled in this spectacular way; it has simply played the role of the
agent by which a certain effect is transmitted. And here we see the essential
feature of what is called wave motion. A condition of some kind is transmitted
from one place to another by means of a medium, but the medium itself is not
transported. A local effect can be linked to a distant cause, and there is a time lag
between cause and effect that depends on the properties of the medium and finds
its expression in the velocity of the wave. All material media--solids, liquids, and
gases--can carry energy and information by means of waves..."Although waves
on water are the most familiar type of wave, they are also among the most
complicated to analyze in terms of underlying physical processes. We shall,
therefore, not have very much to say about them. Instead, we shall turn to our
old standby--the stretched string--about which we have learned a good deal that
can now be applied to the present discussion."