Warm-Up Exercise 21

Due 12:15 pm, Mon 15 Oct 2012

Physics 123, Fall 2012

Reading assignment: PpP 4.1,5.1

PpP states that "a pure sine wave has a precisely defined frequency... but a completely undefined position." What does it mean to have a "completely undefined position"?

PpP states that "the 'envelope' of the wave... can travel at a different speed than the ripples inside of the envelope." That was a very hard concept for me to grasp when I was a student, but fortunately computer animation has come a long way since then. Browse to http://en.wikipedia.org/wiki/Group_velocity, and look at the first two figures of the page. (I actually created the second figure myself.) Observe that the envelope and the ripples are indeed traveling at different speeds! For each figure, measure the speed of travel on your monitor (cm/s) for both the envelope and the ripples.