1 Physics 7C SS1 Lecture 1: Waves Dr. Emily West

2 Agenda Logistics: Syllabus and Web Page Clicker Setup Course Overview--the models of 7C Simple Harmonic Motion Review Wave Introduction

3 Course webpage

4

5

6

7

8 Clicker Setup: Joining Class 1)Turn on your clicker; it scans for classes 2)If it doesn’t scan automatically, hit enter (green button) 3)Find 09SS1PHY7C; hit enter 4)Display reads “ANS: 09SS1PHY7C;” hit enter 5)When you’ve successfully joined, display reads “ANS: wait for Q”

9 Clicker Setup: Student ID 1)Turn on your clicker 2)Press * to access Setup Menu 3)Scroll to find “ID;” hit Enter (green button) 4)Enter your Student ID so I can give you credit; hit enter

10 Check Clicker Setup When did you take 7B? a)Spring 09 b)Winter 09 c)Fall 09 or earlier d)Didn’t take 7B (but took 7A) e)I haven’t taken any 7-series classes

11 Course Overview: Models of 7C Wave Model Waves in 1, 2, and 3 dimensions Interference Ray Model Reflection & Refraction Lenses Field Model Electricity Magnetism

12 Simple Harmonic Motion Review How can we describe the motion of oscillating objects?

13 Simple Harmonic Motion (SHM) Constructs Amplitude: maximum distance from equilibrium Period (or frequency): amount of time required to complete a cycle (or number of cycles per unit time) Equilibrium: position at which all forces acting on the object sum to zero. Displacement: position of the object relative to equilibrium Restoring Force: a force that acts on an object that tends move it toward equilibrium Defining SHM: The restoring force is proportional to the displacement. Anything missing?

14 Mathematics of SHM y=Displacement A=Amplitude T=Period t y

15 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… Displacement?

16 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… Amplitude?

17 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… Period?

18 Mathematics of SHM y=Displacement A=Amplitude T=Period t y y(t) = A sin (2 t/T)??? In this image, what is the mass doing at t=0 seconds? A T T A Is the equation correct as is?

19 Mathematics of SHM y=Displacement A=Amplitude T=Period t y y(t) = A sin (2 t/T + ) In this image, what is the mass doing at t=0 seconds? In this image, what value does  have? T  =phase y(t) = A sin (2 t/T)? A

20 Introduction to Waves

21 Questions to consider about waves… What new constructs are needed to describe waves? What constructs can I control when I start the wave? What constructs are set by the medium that carries the wave? What moves from one end of the machine to the other?

22 Definition of Wave Waves: A transfer of energy without bringing along the mass. Particles in the medium get disturbed and collide, but they stay oscillating about one position; they don’t travel with the wave. The medium does not effectively move. The disturbance advances, that’s the wave.

23 A vibrating object acts as the source of the wave. As a speaker moves through a cycle, it fixes the period and frequency. A = Amplitude, controlled by what starts the wave T = Period, how long to get back to where it started = Wavelength, repeat distance in space T = where f is the frequency Velocity v = f (note meters per second)