Honors Physics 5-3-16

Waves and

Sound

PhET Simulation

1. https://phet.colorado.edu/sims/html/wave-

on-a-string/latest/wave-on-a-

string_en.html

2. Wave on a string

3. https://phet.colorado.edu/en/simulations/c

ategory/physics/sound-and-waves

wave

• Wave: A brief introduction to transverse wave (5 minute)

• Transverse and Longitudinal Waves by B-science

• Waves by B-science

• https://www.youtube.com/watch?v=jAXx0018QCc

(Transverse and Longitudinal Waves in Physics)

• The Coolest Things Sound Waves Do

• Applications of reflection of sound waves

• Science - Transmission of Sound

• The Doppler Effect: what does motion do to waves

• doppler effect, shock wave , and sonic boom

(https://www.youtube.com/watch?v=I1ykNQijOC8 )

Defining Pulse and Wave

1. A pulse is a single disturbance which carries energy through a

medium or through space. Example is pulse travelling down the

slinky

2. A wave is a repeated disturbance which carries energy. The mass

of the slinky doesn't move from end of the slinky to the other, but

the energy it carries does.

3. A wave is a traveling disturbance.

4. A wave carries energy from place to place.

Reflection of Pulse

• When a pulse or wave reaches a hard

boundary, it reflects off the boundary, and

is inverted.

• If a pulse or wave reaches a soft, or

flexible, boundary, it still reflects off the

boundary, but does not invert

Types of waves: Mechanical Vs. Electromagnetic

• mechanical wave: Are waves that requires a medium

(or material) through which to travel.

– Examples: water waves,

– sound waves,

– slinky waves,

– and even seismic waves.

• Electromagnetic waves: Are waves that do not require

a medium in order to travel.

– Electromagnetic waves (or EM waves) are considered part of the

Electromagnetic Spectrum. Examples of EM waves include:

• light (infra red light, visible light, ultraviolet)

• radio waves,

• microwaves,

• X-rays and Gamma rays

1. Transverse Wave

Classification of waves upon direction of vibration:

Transverse Vs Longitudinal Wave

Waves in which the particles of the wave vibrate/oscillate perpendicular to

the wave's direction of motion are known as transverse waves.

Examples of transverse waves include :

(1)seismic S waves,

(2) electromagnetic waves,

(3) and even stadium waves (the "human" waves you see at a baseball or

football game!).

Longitudinal Wave

Waves in which the "particles" of the wave vibrate in the

same direction as the wave direction are known

as longitudinal waves, or compressional waves , or

Pressure waves.

Examples of longitudinal waves include sound waves

and seismic P waves.

Some Waves, e.g Water waves, are partially

transverse and partially longitudinal.

Periodic Waves consist of cycles or patterns that are produced

over and over again by the source.

Periodic waves or Repeated Waves:

Crest, trough, In phase and out of phase

• The highest points on the wave are known as crests.

• The lowest points on the wave are known as troughs

• Points on the same wave with the same displacement from

equilibrium moving in the same direction (such as a crest to

a crest or a trough to a trough) are said to be in

phase (phase difference is 0° or 360°).

• Points with opposite displacements from equilibrium (such

as a crest to a trough) are said to be 180° out of phase.

• Question: The diagram represents a periodic

wave. Which point on the wave is in phase with

point P?

• Question: Two waves having the same

frequency and amplitude are traveling in the

same medium. Maximum constructive

interference occurs at points where the phase

difference between the two superposed waves

is: (C , P, 0)

Characteristic of Periodic Waves

In the drawing, one cycle is shaded in color.

The amplitude The amplitude of the wave, corresponding to

the energy of the wave, is the distance from the baseline to a

crest or the baseline to a trough. It is the maximum distance of

particle of the medium from the particles undisturbed position.

The wavelength is the horizontal length/distance of one cycle of

the wave and has unit of metres.

The period is the time required for one complete cycle.

The frequency is related to period and has units of Hz, or s-1.T

f1

Speed of Waves (v)

)(*)()/(

wavelenthffrequncyperiodwavelethspeed

fT

v

Question : The Wavelengths of Radio Waves

AM and FM radio waves are transverse waves consisting of electric and

magnetic field disturbances traveling at a speed of light c=3.00x108m/s. A station

broadcasts AM radio waves whose frequency is 1230x103Hz and an FM

radio wave whose frequency is 91.9x106Hz. Find the distance between

adjacent crests in each wave.

fT

v

f

v

16.2 Periodic Waves

AM m 244Hz101230

sm1000.33

8

f

v

FM m 26.3Hz1091.9

sm1000.36

8

f

v

Sound Wave• Sound is a mechanical wave which we observe by detecting vibrations in

the inner ear.

• Sound can travel through other media as well, including water, wood, and

even steel.

• The particles of a sound wave vibrate in a direction parallel with the

direction of the sound wave's velocity, therefore sound is a longitudinal

wave.

• The speed of sound in air at standard temperature and pressure (STP) is

approximately 331 m/s.

• When we observe sound waves through hearing, we pick up the amplitude,

or energy, of the wave as loudness. The frequency of the wave is perceived

as pitch, with higher frequencies observed as a higher pitch.

• Certain devices create strong sound waves at a single specific frequency. If

another object, having the same "natural frequency," is impacted by these

sound waves, it may begin to vibrate at this frequency, producing more

sound waves. The phenomenon where one object emitting a sound wave

with a specific frequency causes another object with the same natural

frequency to vibrate is known as resonance..

The Nature of Sound Waves

LONGITUDINAL SOUND WAVES

The distance between adjacent condensations is equal to the

wavelength of the sound wave.

Wavelength of sound wave

The Nature of Sound Waves

Individual air molecules are not carried along with the wave.

The Nature of Sound Waves

THE FREQUENCY OF A SOUND WAVE

The frequency is the number of cycles

per second.

A sound with a single frequency is called

a pure tone.

The brain interprets the frequency in terms

of the subjective quality called pitch.

The Nature of Sound Waves

THE PRESSURE AMPLITUDE OF A SOUND WAVE

Loudness is an attribute of

a sound that depends primarily

on the pressure amplitude

of the wave.

The Speed of Sound

Sound travels through gases,

liquids, and solids at considerably

different speeds.

stop

The Speed of Sound

Conceptual Problem: Lightning, Thunder, and a Rule of Thumb

There is a rule of thumb for estimating how far away a thunderstorm is.

After you see a flash of lighting, count off the seconds until the thunder

is heard. Divide the number of seconds by five. The result gives the

approximate distance (in miles) to the thunderstorm. Why does this

rule work?

Sound Intensity

Sound waves carry energy that can be used to do work.

The amount of energy transported per second is called the

power of the wave.

The sound intensity is defined as the power that passes perpendicularly

through a surface divided by the area of that surface.

A

PI

Sound Intensity

Example Sound Intensities

12x10-5W of sound power passed through the surfaces labeled 1 and 2. The

areas of these surfaces are 4.0m2 and 12m2. Determine the sound intensity

at each surface.

Answer: Sound Intensity

25

2

5

1

1 mW100.34.0m

W1012

A

PI

25

2

5

2

2 mW100.112m

W1012

A

PI

Sound Intensity

For a 1000 Hz tone, the smallest sound intensity that the human ear

can detect is about 1x10-12W/m2. This intensity is called the threshold

of hearing.

On the other extreme, continuous exposure to intensities greater than

1W/m2 can be painful.

If the source emits sound uniformly in all directions, the intensity depends

on the distance from the source in a simple way.

Sound Intensity

Conceptual Example Reflected Sound and Sound Intensity

Suppose the person singing in the shower produces a sound power P.

Sound reflects from the surrounding shower stall. At a distance r in front

of the person, does the equation for the intensity of sound emitted uniformly

in all directions underestimate, overestimate, or give the correct sound

intensity?

24 r

PI

The Doppler Effect

The Doppler effect is the change in

frequency or pitch of the sound

detected by an observer because the

sound source and the observer have

different velocities with respect to the

medium of sound propagation.

Applications of Sound in Medicine

By scanning ultrasonic waves across the body and detecting the echoes

from various locations, it is possible to obtain an image.

Applications of Sound in Medicine

Ultrasonic sound waves cause the tip of the

probe to vibrate at 23 kHz and shatter

sections of the tumor that it touches.

Applications of Sound in Medicine

When the sound is reflected from the red blood cells, its frequency is

changed in a kind of Doppler effect because the cells are moving.