Chapter 11 Physics Tiffany Rhodes Chapter 11 Physics Tiffany Rhodes

Huge Wave!

 What do you think of when you hear the word “Waves”? sound waves, light waves, radio waves, microwaves, water waves, sine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, slinky waves Wavelike phenomena = pendulum, child on a swing, waving to your neighbor

Topics Covered  1. Wave definition  2. Medium  3. Simple Harmonic Motion  4. Period/ Frequency  5. Types and Anatomy of Waves  6. Amplitude  7. Speed of Waves  1. Wave definition  2. Medium  3. Simple Harmonic Motion  4. Period/ Frequency  5. Types and Anatomy of Waves  6. Amplitude  7. Speed of Waves

1. Wave Definition  How do you create a water wave? Created by a disturbance Example: Throwing a rock into water

Definition  Waves are a transfer of energy in the form of a disturbance or vibration  Usually through a material substance  Cannot exist in one place  Must extend from one place to another  Transfer energy! NOT MASS!!  Waves are a transfer of energy in the form of a disturbance or vibration  Usually through a material substance  Cannot exist in one place  Must extend from one place to another  Transfer energy! NOT MASS!!

2. Medium  The material the wave travels through  The type of disturbance and medium determine the kind of wave  The material the wave travels through  The type of disturbance and medium determine the kind of wave Disturbance in…Kind of Wave Gas, solid or liquid particlesSound Surface of fluid“wave” Electromagnetic Field“light” Ground (Earth)Seismic

Medium

3. Simple Harmonic Motion

Periodic Motion – If an object oscillates back and forth over the same path, each cycle taking the same amount of time Simple Harmonic Motion – Periodic Wave Characteristics

Simple Harmonic Motion Displacement is measured from the equilibrium point Amplitude is the maximum displacement A cycle is a full to-and-fro motion Period is the time required to complete one cycle Frequency is the number of cycles completed per second

Pendulums are useful in understanding waves: Simple harmonic motion (Periodic) Creates a special curve known as a SINE CURVE : Sine Curve is a pictorial representation of a wave.

4. Period/ Frequency

 Frequency(period)- determined by source only  Not affected by changes in speed  Not affected by changes in wavelength  Frequency(period)- determined by source only  Not affected by changes in speed  Not affected by changes in wavelength 4. Period/ Frequency

PENDULUMS: What is one cycle of a pendulum? What is the period of a pendulum? Units? What affects the period of the pendulum? What is the frequency of the pendulum? Units?

Frequency = cycles / time Frequency = 1 / period HERTZ, Hz Period = time/ cycles Period = 1 / frequency SECONDS, s

EX: A pendulum completes 30 cycles in 15 seconds. Calculate its frequency and its period. F = cycles/ time 30 cycles / 15 seconds = 2.0 hz Period = time / cycles 15 sec/ 30 cycles = 0.5 seconds RECIPRICALS!!! Reciprocals! ½ = 0.5 1/0.5 = 2

6/14/ Homework Worksheet Pg 309 #1-4

Waves Introduction Continued…

5. Types and Anatomy of Waves

2 Common Types  I. Transverse  II. Longitudinal  I. Transverse  II. Longitudinal

I. TRANSVERSE

The Anatomy of a Wave

Transverse Wave

II. Longitudinal

Parts of a longitudinal wave  Compression - maximum density  Rarefaction - minimum density  Compression - maximum density  Rarefaction - minimum density

Ex: sound - vibrating prongs of a tuning fork wavelength is the distance from compression to next compression or from a rarefaction to rarefaction.

6. Amplitude

Amplitudes  Based on Amount of Energy  A high energy wave is characterized by a high amplitude;  a low energy wave is characterized by a low amplitude  Based on Amount of Energy  A high energy wave is characterized by a high amplitude;  a low energy wave is characterized by a low amplitude

Amplitude:  Amplitude- determined by source (and medium)  Affected by amount of energy  If energy decreases (friction), amplitude decreases  In an ideal wave, using same medium, amplitude will not change regardless of speed, wavelength, or frequency changes  Amplitude- determined by source (and medium)  Affected by amount of energy  If energy decreases (friction), amplitude decreases  In an ideal wave, using same medium, amplitude will not change regardless of speed, wavelength, or frequency changes

 Wavelength - affected by changes in frequency and speed 7. Wavelength

8. Speed of Waves

 Speed of Wave- determined by medium  Not affected by changes in amplitude  Not affected by changes in frequency  Speed of Wave- determined by medium  Not affected by changes in amplitude  Not affected by changes in frequency 8. Speed of Waves

How can you determine the speed of the wave? Distance = wavelength(m) time = period(s) 1. Measure distance between 2 points of the wave 2. Measure the time it takes one pulse of the wave to travel that distance 3. Divide = meters per second

Wave Equation = wavelength (m) f = frequency (cycles/sec) V = speed (m/s) = wavelength (m) f = frequency (cycles/sec) V = speed (m/s)

1. So the lifeguard notices that the water wave has a wavelength of 0.5 m and 2.5 crests passed by the buoy each second, what is its speed?

Sample Problem #2 2. Wavelength in a water wave is 4.0 m, and the crest travels 9.0 m in 4.5 s. What is the frequency of the wave?

Slinky Next Class: Good Vibrations Lab Classwork: Speed of Wave Wkst