If we take one end of a taught spring or rope and move it in simple harmonic motion, a wave travels down the spring or rope.  The distance over which a wave travels before it repeats itself is called the wavelength and is represented by the Greek letter lambda (λ).  Time time over which a wave travels before it repeats itself is the period T.  The velocity of a wave is the ratio of the distance it travels over the time it takes, so v = λ/T = λf.  When waves in a spring or rope hit the other end they reflect.

			The equation for a wave traveling to the right (increasing x) is:

			The graphs below show the wave above moving to the right at 0.5 second intervals:

			The equation for a wave traveling to the left (decreasing x) is:

			The graphs below show the wave above moving to the left at 0.5 second intervals:

			The sum of a wave traveling to the right and an identical wave traveling to the left at the same speed is a standing wave -- where the amplitude just goes up and down without any apparent sideways motion to the left or the right.

			Read pp. 378-400 of the text.

			Answer the questions in HW 20 on WebAssign:  http://webassign.net/login.html