1. 1 Physics 7C SS1 Lecture 1: Waves Dr. Emily West ewest@physics.ucdavis.edu

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

3. 3 Course webpage http://physics.ucdavis.edu/physics7

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8. 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. 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. 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. 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. 12 Simple Harmonic Motion Review How can we describe the motion of oscillating objects?

13. 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. 14 Mathematics of SHM y=Displacement A=Amplitude T=Period t y

15. 15 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… Displacement? 1 4 3 5 2 6

16. 16 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… 1 4 3 5 2 6 Amplitude?

17. 17 Mathematics of SHM y=Displacement A=Amplitude T=Period t y In this image, which numbers, if any, show… 1 4 3 5 2 6 Period?

18. 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. 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. 20 Introduction to Waves

21. 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. 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. 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)