Sound Wave Properties Sound - PowerPoint Presentation

Slide1

Sound Wave Properties

Slide2

Sound

Sound is a

longitudinal

(Mechanical)wave caused by a

vibrating

object

Molecules

collide

, producing sound

Examples:

Vocal chords

, guitar or piano strings, tuning fork, etc.

Slide3

Longitudinal Wave

Referred to as a

PRESSURE WAVE

A sound wave has

high

pressure and low pressure regions moving through a mediumThe high pressure regions are called compressions, molecules are compressedThe low pressure regions are called rarefactions, molecules are spread out

Slide4

Slide5

Frequency

The frequency of a sound wave (or any wave) is the number of complete

vibrations

per

second

.The frequency of sound determines its pitchThe higher the frequency, the higher the pitchThe lower the frequency, the lower

the pitch

Slide6

Wavelength

Wavelength is the

distance

between two high pressures or two low pressures

Wavelength and frequency are

inversely relatedA short wavelength (high frequency) results in a high pitchhttp://phet.colorado.edu/en/simulation/sound

Slide7

Slide8

Frequency and the human ear

Humans can hear a range of frequencies from

20 Hz

to

20,000 Hz

The older you get, the hearing range shrinksSound waves with frequencies below 20 Hz are called infrasonicSound waves with frequencies above 20,000 Hz are called ultrasonic

Slide9

Amplitude

The

AMPLITUDE

of a sound wave determines it’s loudness or softness

This means the more

energy in a sound wave, the louder the soundSound intensity is a measure of how much energy passes a given point in a time periodIntensity is measured in decibels

Slide10

Slide11

Sound Behaviors: Reflection

Reflection of sound results in an

echo

Sound waves leave a source, travel a distance, and

bounce

back to the originAnimals, like bats, uses echoes to locate preyOther uses include determining distance between objects, echocardiogramsThe distance the sound travels to get back to the origin is 2x the distance between the sound source and boundary

Slide12

Sound Behavior: Refraction

Refraction occurs when sound moves from one

medium

to another

The wave bends, and the speed

changes

Even when sound moves from

warmer

areas to

cooler

areas, refraction occurs

Slide13

Sound Behavior: Diffraction

Diffraction

occurs when sound waves pass through an opening or through a barrier

Low

pitched sound waves travel

farther than high pitched sound wavesAnimals use diffraction for communication

Slide14

Velocity

Velocity of sound depends on the

medium

it travels through and the

phase

of the mediumSound travels faster in liquids than in air (4 times faster in water than air)Sound travels faster in solids than in liquids (11 times faster in iron than in air)Sound does not travel through a vacuum (there is no air so sound has no medium)

Slide15

Velocity and Temperature

In air at room temperature, sound travels at

343 m/s

(at 20°C). This is about 766 mph.

As temperature increases, the velocity of sound increases

v= velocity of sound in airT=temperature of air in °C

v=331 + (0.6)T

Slide16

Wave Equation

The basic wave equation is also applied to sound

V= velocity, measured in

m/s

λ

= wavelength, measured in

meters

f= frequency, measured in

hertz

 

Slide17

Bellwork

What type of wave is a sound wave?

What is a compression? Rarefaction?

Based on yesterday’s class, state the relationship between wavelength and the pitch of a sound wave.

Explain in one sentence how blowing across a straw produces a sound.

How can you change the loudness of a sound you produce?

Slide18

Example Problems:

Sound

waves travel at approximately 340 m/s. What is the wavelength of a sound wave with a frequency of 20 Hz?

What is the speed of sound traveling in air at 20º C?

If the above sound wave has a frequency of 261.6 Hz, what is the wavelength of the wave?

Slide19

What is the Doppler Effect?

http://molebash.com/doppler/home.htm

Slide20

Doppler Effect

Sound waves move out in all directions

Slide21

Definition

The Doppler effect is a change in the

apparent

frequency due to the

motion

of the source or the receiverExample: As an ambulance with sirens approaches, the pitch seems high. As the ambulance moves by the pitch lowers.

Slide22

Doppler Effect

As the wave travels outward, the

front

of the wave bunches up, producing a

shorter

wavelengthWe hear a higher frequency

Slide23

The back of the wave

spreads

out, producing a

longer

wavelength

We hear a lower frequencyhttp://www.sounddogs.com/searchresults.asp?Keyword=Doppler

Slide24

Observer

A

hears a

low

pitch (lower frequency)

Observer

B

hears the

correct

pitch (no change in frequency)

Observer

C

hears a

high

pitch (high frequency)

Slide25

When the source goes faster, the wave fronts in the front of the source start to bunch up closer and closer together, until...

Slide26

The object actually starts to go faster than the speed of sound. A

sonic boom

is then created.

Slide27

Uses of the Doppler Effect

Police

use

D

oppler to measure your speed with radar

A frequency is sent out with a radar gunThe sound wave hits your car and bounces back to the police carSpeed can be determined based on the frequency changes receivedRadar can be used to determine the speed of baseballsAstronomers can determine the distance to other galaxiesBats use Doppler to locate preyIf the bat is catching the prey, the frequency is high

If the prey is moving away from the bat, the frequency is low

Slide28

Doppler Equation

= frequency detected by observer

= frequency produced by the source

= velocity of the sound wave

= velocity of the detector (observer)

= velocity of the source

 

Slide29

Things to remember

The velocity detected by the observer (

v

d

) is

negative if the observer moves away from the sourceThe velocity detected by the observer (vd) is positive

is the observer moves

toward

the source

The velocity of the source (

) is

negative

if the source moves

toward

the observer

The velocity of the source

(

)

is

positive

if the source moves

away

from the observer

 

Slide30

Example

A trumpet player plays a C note of 524 Hz while traveling in a convertible at 24.6 m/s. If the car is coming toward you, what frequency should you hear? Assume the temperature is 20°C.

Slide31

Homework

p

.405 # 1-5 (use table 15-1 for the speed of sound in various media)

p. 409 #6-8 Read Carefully!

Slide32

Hearing Range Frequencies

http://www.movingsoundtech.com

/

http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test

/