# Physics Unit 12: Waves and Harmonic Motion

Intro to sound ad waves. Covers amplitude, wavelength, frequency, wave velocity.  Includes CA std.  Includes Electra Spectra video, phet wave simulator and lightning sound delay.

### Unit 11: Waves and Sound – Weeks 3-4

Standard: 4 a-d, f What are waves?
Waves carry energy
Transverse and longitudinal waves, seismic and ocean waves
Wavelength, frequency, and wave velocity
Sound waves, music
Beats, diffraction, refraction, resonances
The Doppler Effect

Lesson 1: Wed 1/21/15

Warm up: {FM, Pred., diagnostic} Name and sketch 3 kinds of waves.

What you need to know:
Definitions:
Amplitude {A}: the greatest extent or movement from the center-line of the wave, essentislly the midpoint to maximum height measurement.
Wavelength {λ}: The distance between adjacent corresponding points on a wave. Example: the distance from one peak to the next peak or the distance from one trough to the next trough in a wave. Note: The distance from where the wave height is zero to the next is only half a wavelength.
Frequency {f  or  ν (greek letter nu)}: The number of waves generated per second in Hz (Hertz or 1/seconds).

Wave velocity {v or c for light}: The speed at which a wave moves through a medium (OK so we learned in Unit 10 that light doesn’t need a medium but just go with it for now).

Formulas:

v = λ f

Wave simulator: try it, change the controls!

Using v (sound in air at 25 °C) = 346 m/s, calculate how long it takes for sound to travel 1 meter, 1 km, 3 km. Note that the speed of sound in air is approximately 1100 ft/sec.

Lightning – light + thunder
We’ll try to estimate the time delay between the flash of light and the sound.  Start to count when you see a lightning flash. The number of seconds it takes for the thunder to reach you tells you your distance from the lightning strike. (ex. 5 sec -> distance approximately 5500 feet or 1 mile)

Using the data from the video, calculate the distance from the lightning strike to the observer.

Lesson 2:

Warm Up: From Memory, write an equation and determine the distance to a lightning strike if it takes 4 seconds from the time you see the lightning to the moment when you hear the thunder.

Problem: While the speed of sound on the Earth is 346 m/s,  the speed of sound on Mars is lower. Since Mars is a smaller planet than Earth it has a less dense atmosphere.  It turns out the speed of sound on Mars is only 244 m/s.

You are a Martian Explorer establishing an outpost on Mars. You are cautious and need to decide if you must return to your shelter. A lightning strike is followed by thunder after a time delay of 4 seconds.

How far away is the storm?

Modeling: Example Problem 3 pg 392

GP: / IP: Practice problems 15-25 pg 393 – finish for homework.

Exit Assessment: Sketch a wave showing amplitude, wavelength, annotated with speed of propagation and frequency.

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Lesson 3:

Warm up: {FM}
Name and sketch 3 types of waves. Which type of wave is sound? ocean waves?

Reading Ch 14 Section 2: (we’ll go back tp section 1 later.

Modeling: Examle problem 3 pg 392

GP: Paractice problem 15 pg 393

IP: Practice problems 16 – 25 – finish for HW.

XA: Write down equation relating wave speed to wqavelength and frequency.

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A simple – quick demonstration of constructive ad destructive interference;

Refraction:

Lesson 4:

In previous class lectures we learned about the superposition principal for waves. From the textbook we learned about sound waves in tubes, pressure and displacement – nodes and antinodes.

In this video, sound waves are generated in a tube filed with propane. Flames are highest at the dispacement (nodes or antinodes). Write the answer in your notebook.

Watch the film again. This time stop the film when the frequency is 399 Hz. Notice the 100cm marker. Using this data and spacing between antinodes, calculate the speed of sound in the propane filled tube. (hint: remember that the distance between antinodes is actually 1/2 the wavelength)