PHY138 – Waves, Lecture 2 “Physics is like sex: sure, it may give some practical results, but that’s not why we do it.” - Richard Feynman, Nobel Laureate

Reading Assignment Please read the following from Serway and Jewett before class on Monday: Chapter 13, up to and including Section 13.5 A www.masteringphysics.com problem set on Chapter 12 is due on Friday at 5:00PM

Last day’s lecture: some comments S.H.M. is not constant acceleration, or constant force – both vary with time. S.H.M. results when restoring force is proportional to displacement. Other types of oscillatory motion are possible, but not discussed in this course. Angular frequency ω = 2π/T, where T=period. (T = 2π/ω) “frequency” f = 1/T (in Hertz)

PHY138 – Waves, Lecture 2 Today’s overview Energy in S.H.M. The Simple Pendulum Resonance Waves Introduction, Chapter 13

Interesting points in S.H.M. When x=A cos (ωt) (phase constant=0) K = kinetic energy, U = potential energy t x v a K U +A -ω2A ½kA2 T/4 -ωA T/2 -A +ω2A 3T/4 +ωA T

Quiz An object hangs motionless from a spring. When the object is pulled down, the sum of the elastic potential energy of the spring and the gravitational potential of the object 1. increases. 2. stays the same. 3. decreases.

Mass on Spring versus Pendulum Mass on a Spring Pendulum Condition for S.H.M. Small oscillations Small angles Angular frequency Period

Transverse Wave Motion:

Longitudinal Wave Motion Compressed Compressed Stretched Stretched