1. 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

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

3. 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)

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

5. 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

6. 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.

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

8. Transverse Wave Motion:

9. Longitudinal Wave Motion
Compressed
Compressed
Stretched
Stretched