1. Clicker Question Room Frequency BA
A kid is swinging on a swing with a period T. A second kid climbs on next to the first, doubling the weight on the swing. The period of the swing is now...
the same, T
B) 2T C)
D) none of these.
The period of a simple pendulum does not depend on the mass

2. Announcements FCQs for the course will be administered Friday, Dec 2nd
CAPA assignment #14 is due on Friday at 10 pm.
This week in Section: Lab #6 (with prelab)
Next week: Review in Section, Make-up Labs arranged in other sections. Contact your TA this week to arrange a make-up lab. Last chance to make up labs! 5 labs must be completed in order to pass this course.
Detailed Reading Assignments:
Sections , ,
Sections ,
Sections 13.1,13.2,
Sections

3. Final Exam News Final Exam is Tuesday morning, Dec 13, 10:30am – 1pm
Exam will be held in Coors Event Center, more details next week
Practice Exams and Formula sheet will be posted on Monday Dec 5th
Prof. Nagle will hold a review session on Thursday evening, Dec 8th, 7-9pm, in this room (Duane G1B30).
Exam coverage is cumulative!

4. Wave Basics – Taxonomy I
Two Basic Types: Impulse and Periodic v
Impulse on Rope
Periodic on Rope v
Sinusoidal on Rope v

5. Wave Basics – Taxonomy II
Two types of Wave Motion of Medium: Longitudinal and Transverse
Transverse
Wave
Longitudinal
Wave

6. Wave Examples Some common examples of waves are
Sound waves (pressure waves) in air (or in any gas or solid or liquid) – Longitudinal in gas/liquid, both transverse and longitudinal in solid
Waves on a stretched string – Transverse
Waves on a slinky – Transverse and Longitudinal
Waves on the surface of water - Transverse and Longitudinal
"The Wave" at the ballpark stadium. The medium is the people – Transverse
Electromagnetic waves (light) – this is the only kind of wave which does not require a medium! Their properties indicate they are transverse, but you’ll learn more on EM waves next semester.

7. Clicker Question Room Frequency BA
The graph below shows a snapshot of a wave on a string which is traveling to the right. There is a bit of paint on the string at point P.
At the instant shown, the velocity of paint point P has which direction?
E) None of these v x y

8. Clicker Question Room Frequency BA
The graph below shows a snapshot of a wave on a string which is traveling to the right. There is a bit of paint on the string at point P.
At the instant shown, the acceleration of paint point P has which direction?
E) None of these v x y
Steep slope on the wave form means high velocity of paint point, slope in getting larger in magnitude

9. Description of Periodic Waves
Periodic waves are described in terms of three basic quantities:
Wavelength λ, Period T, and amplitude A: λ v 2A
Period T for one piece of medium to complete a motion cycle
All waves move through medium with a speed v which is characteristic of the medium, and this is related to λ and T:
It take time T for the wave to travel distance λ:

10. Frequency and Wave Number Periodic Waves
We can use inverse quantities to describe periodic waves:
Frequency f = 1/T so we can also write: v = λf
Angular Frequency ω = 2π/T = 2πf so we can write : v = λω/2π λ v
Period T for one piece of medium to complete a motion cycle
A new inverse quantity is the wave number k = 2π/λ.
Long wavelength λ gives small wave number k.
We now can write three more relations:
Always check units!!!

11. Wave speeds
In most cases, the wave speed v does NOT depend on f or λ; it just depends the type of medium and how it is excited.
This immediately implies that since v =λf, and v is constant, then large λ corresponds to small f and small λ corresponds to high f.

12. Clicker Question Room Frequency BA
Three waves are traveling along identical strings (same mass per length, same tension, same everything). Wave B has twice the amplitude of the other two. Wave C has 1/2 the wavelength than A or B. Which Wave goes slowest? A B C D) All have same v
Identical string conditions give identical v

13. Clicker Question Room Frequency BA
Three waves are traveling along identical strings (same mass per length, same tension, same everything). Wave B has twice the amplitude of the other two. Wave C has 1/2 the wavelength than A or B. Which wave has the highest frequency? A B C D) All have same f
No dependence on amplitude
Smallest wavelength λ gives highest frequency f

14. Wave Interference
Superposition Principle: If two or more waves are present in the same place, at the same time, the total wave is the sum of the individual waves: ytot(x,t) = y1(x,t) + y2(x,t). You get constructive or destructive interference depending on whether y1 and y2 add (both have same sign) or cancel (opposite signs).
We can see this in the simuation

15. Standing Waves
Two sinusoidal traveling waves of the same λ (and therefore the same f = v/λ ) and the same amplitude, traveling in opposite directions, overlapping in the same region of space, make a standing wave. m x
nodes
anti-nodes λ
ends fixed L
We can see this in both the simulation and a rope!

16. Clicker Question Room Frequency BA
A string is clamped at both ends and then plucked so that it vibrates in a standing mode between two extreme positions A and C. Let upward motion correspond to positive velocities. When the string is in position B, the instantaneous velocity of points along the string is…
A) zero everywhere. B) positive everywhere.
C) negative everywhere. D) depends on the position.
No dependence on amplitude

17. Wave Simulations