Waves and Sound

Part 1

Intro

Write the following questions on a blank piece of paper (don’t answer yet)

1. What is the difference between a mechanical and

electromagnetic wave?

2. What is the difference between a transverse and

longitudinal wave?

3. What do all waves transfer?

4. What don’t waves transfer?

• 23) analyze the properties of waves (GPS, HSGT)

• 23a) describe waves as a means of transporting energy (GPS)

• 23b) explain the production and propagation of waves created by simple harmonic motion (i.e., pendulum/spring motion) (GPS)

• 23c) compare and contrast mechanical and electromagnetic waves (GPS)

• 23d) compare and contrast longitudinal and transverse waves (GPS)

• 23e) explain the relationship between wavelength, frequency and wave speed (GPS)

• 23f) demonstrate and explain the general wave properties of reflection, refraction, interference and diffraction (GPS)

• 23g) explain the relationship between the phenomena of interference and the principle of superposition (GPS)

• 23h) demonstrate and explain wave phenomena using various types of equipment (i.e., ripple tank, slinky, soft rope, signal generator and oscilloscope) (GPS)

• 24) analyze the properties of sound (GPS, HSGT)

• 24a) explain the relationship between wavelength, frequency, period and wave speed as applied to sound waves (GPS)

• 24b) demonstrate apparent frequency changes due to Doppler Effect (GPS)

• 24b1) solve problems of apparent frequency changes due to Doppler Effect (GPS)

• 24c) use the law of reflection as it applies to echoes (GPS)

• 24d) explain the relationship of the speed of sound to temperature and elasticity of a medium (GPS)

• 24e) illustrate interference of sound waves to produce harmonics and resonance in various types of musical instruments, sound recordings, stringed instruments, open and closed pipes, and percussion (GPS)

• 24f) identify ranges for infrasonic, ultrasonic, and audible sounds

• 24g) describe applications of sound to sonar, ultrasound, and bats (GPS)

Section 1: Intro to Waves

• Waves

– Are disturbances that move through an empty space

or through medium (material)

– Waves transfer energy without transferring matter.

– Particles of medium move in simple harmonic motion

Mechanical: Through a medium Electromagnetic:

Through empty space

• Mechanical wave:

– Caused by a disturbed medium and move by action

reaction of particles

– ex: water wave, sound

• A medium is matter particles like gas (ex. air),

liquid (ex. Water), and solid (ex. earth)

Two types of mechanical waves that require a medium

Transverse

Wave

Longitudinal

Wave

Electromagnetic wave:

• Move through empty space (no medium)

• Created by moving electrons

• Ex. radio waves, microwaves, light

Through empty space

Types Electromagnetic Waves

• In order to start and transmit a wave, a

source of disturbance (vibration) and a

disturbed medium are required.

• Mechanical caused by vibrating particles

– Like seen here

• Electromagnetic by vibrating electrons

Damping:

• A decrease in the amplitude of a wave

• Caused by energy loss or the spreading

out of the wave over a larger area.

• Wave pulse is a single wave disturbance

• Wave train (continuous wave) - is a

series of pulses at intervals

Section 2: Types of Mechanical

Waves

Transverse

Longitudinal

Transverse Wave:

• Wave particles move perpendicular to the direction the wave travels

• Ex. vibrating string of a musical instrument

Pe

rpe

nd

icu

lar

to t

he

dir

ec

tio

n o

f tr

ave

l

Direction of

travel

Parts of a transverse wave

Crest

Trough

Equilibrium

Position

Wavelength (ג)

Wavelength (ג)

Wavelength (ג)

amplitude

amplitude

• Crest- highest point on a transverse wave

• Trough- lowest point on a transverse wave

• Equilibrium position- center around which simple harmonic motion occurs

• Amplitude- from the equilibrium position to the crest or trough

Longitudinal Wave:

• Particles vibrate parallel to the direction

the wave travels

• ex. sound wave

Direction of travel

Particles vibrate parallel to the direction of travel

Parts of a Longitudinal Wave:

• Compression- point where the particles

are closest together

• Rarefaction- point where the particles are

furthest apart

Compression

Rarefaction

So, a couple of questions…

1. What starts a wave?

2. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

More Questions

1. What do all waves transfer?

2. What don’t waves transfer?

3. What starts a wave?

4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

More Questions

1. What do all waves transfer? Energy

2. What don’t waves transfer?

3. What starts a wave?

4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

More Questions

1. What do all waves transfer? Energy

2. What don’t waves transfer? Matter

3. What starts a wave?

4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

More Questions

1. What do all waves transfer? Energy

2. What don’t waves transfer? Matter

3. What starts a wave? Disturbance in a medium

4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

More Questions

1. What do all waves transfer? Energy

2. What don’t waves transfer? Matter

3. What starts a wave? Disturbance in a medium

4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

Relationship between

Wavelength, Frequency and

Wave Speed

• velocity ( v ): speed of the wave.

– unit: m/s (meter/second)

• frequency ( f ): vibrations per second of

the wave

– unit: Hz (hertz)

• wavelength ( ג ): length of one wave pulse

– unit: m (meter)

Lets revisit our old equation

What is the velocity of an object that moves

25 meters in 3 seconds?

V= ___ d

t

Lets revisit our old equation

What is the velocity of an object that moves

25 meters in 3 seconds?

V= ___ d

t

Now lets look at the new equation you can

use as well.

V= ___ d

t

old new

Example what is the velocity of a wave that has a

frequency of 3Hz and a wavelength of 5m?

Now lets look at the new equation

you can use as well

V= ___ d

t

old new

Now lets look at the new equation

you can use as well

V= ___ d

t

old new

Now lets look at the new equation

you can use as well

V= ___ d

t

old new

Now lets look at the new equation

you can use as well

V= ___ d

t

old new

Relationship between frequency and

wavelength.

• Wavelength and frequency are inversely

related

• As frequency goes up the wavelength gets

shorter (assuming no change in velocity)

Click for animation

Period (T) vs. Frequency (f)

• Period (T) – seconds for one cycle

– (unit s)

• Frequency (f) – cycles for one second

– (unit Hz)

• If you know one you can solve for the other

Example 1 Wave Math

The frequency of a wave is 560 Hz. What is

its period?

The frequency of a wave is 560 Hz. What is

its period?

Example 2 Wave Math

A girl floats in the ocean and watches 12

wave crests pass her in 46 s. Calculate the

wave: a) frequency b) period

A girl floats in the ocean and watches 12

wave crests pass her in 46 s. Calculate the

wave: a) frequency b) period

Example 3 Wave Math

The period of a wave is 0.044s. How many

cycles will the energy source make in 22s?

cycles

second

The period of a wave is 0.044s. How many

cycles will the energy source make in 22s?

Example 4 Wave Math

A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.

A. What is the wavelength?

B. What is the amplitude?

0.33m

0.24m

Example 4 Wave Math

A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.

A. What is the wavelength?

B. What is the amplitude?

0.33m

0.66m

Example 4 Wave Math

A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.

A. What is the wavelength?

B. What is the amplitude?

0.24m 0.12m

Example 5 Wave Math

What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

Example 5 Wave Math

What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

Example 6 Wave Math

You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m.

A. What is the frequency?

B. What is the period?

C. What is the velocity?

Example 6 Wave Math

You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m.

A. what is the frequency

B. What is the period

C. Velocity

Assignment to work on:

CP

• Worksheet Packet Section 3

Honors

• Worksheet Packet Section 3

• Book Problems 4,5,6 pg 486-487