We have discussed the concept of forces and motion in this course, as well as concepts of energy and momentum.  We have discussed special types of motion – in particular simple harmonic motion in which an object moves in a repetitive fashion characterized by a sinusoidal function. 

We shall now conclude this course with a discussion of another special type of motion.  The strange thing about the motion we are about to discuss is that what is probably the most obvious feature of this motion – a traveling wave – is not really a physical motion at all in the way we are used to speaking of it.  That is, it does not involve an object or material moving from one place to another in the direction of the apparent wave motion.  Instead, what we perceive as wave motion is really the result of the propagation of energy from one position to another within a medium (the material through which the energy signal is propagating).  There are two media (plural of medium)  in particular that we will be considering: waves traveling through strings and through air.  The latter waves, which are really pressure waves, are what we more commonly call sound waves,  and will be the focus of the end of this lecture.