How can I explain the concept of

SOUND, WAVES AND DOPPLER

EFFECT?

WAVES are everywhere. We encounter them

on a daily basis. Examples of waves are:

WAVE - a disturbance traveling through

a medium or in a vacuum from one

location to another.

is the maximum distance

the particles in a wave

vibrate from their rest positions.

- the number of waves

produced in a given time

Frequency= waves/time

SOUND

It is composed of waves of compression and rarefaction in

which the human ear is sensitive

Sound may be described by four perceptual characteristics:

Pitch – refers to the highness or lowness of a sound. It depends upon the

frequency of the sounding object. Higher frequency sounds produce high

pitch while lower frequency sounds produce low pitch.

Loudness – is a physiological sensation that varies from one person to

another. It depends on the sense of hearing, the distance from the source

and the material through which the sound travels.

Pitch

-description of how high or low

the sound seems to a person

. Loudness-how loud or soft a sound is

perceived to be.

Sound Waves – is a longitudinal wave

created by vibrating solids, liquids or gases

and capable of producing a sensation in our

auditory system. It can travel through a

medium from one location to another. It

travels at a speed of 331m/s in air at sea

level when the temperature is 0 degree.

This music is so

loud please turn

it UP…

Loudness of Sound in Decibels

Just like all longitudinal

(compression)waves, sound

Waves possess a velocity,

frequency, wavelength,

phase, period, and amplitude.

Sound waves also reflect,

refract, diffract, and interfere.

2. LOUDNESS or intensity-description of how high or low

the sound seems to a person-determined mainly by the

amplitude of the sound wave

a. Decibel (dB)- unit used to measure sound intensity or loudness.

Speed of Sound

Depends on:1. Type of medium

-travels better through liquids and solids and gas can’t travel through a vacuum.

2. Temperature of medium-travels faster at higher temperature.

3. Density-sound moves well through dense materials.

4. Elasticity-sound waves move fast through

elastic materials

Human Hearingsound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in

cochlea

Ultrasound- sound waves with frequencies above the normal

human range of hearing.

Sounds in the range from 20-100kHz

Infrasound- sounds with frequencies below the

normal human range of hearing.

Sounds in the 20-200 Hz range

DOPPLER EFFECT

The apparent change in the frequency of a source of wave

due to the motion of the source and/or the observer

Developed by Christian Doppler in 1842

The difference of the true frequency and the apparent

frequency is called the Doppler Shift

Doppler Effect

The Doppler effect is the apparent change in the

frequency of sound due to the motion of source of sound

and/or the observer.

The following symbols will be used in the definitions:

fis the true frequency

f’ is the apparent frequency

v is the velocity of the sound (air)

vs is the velocity of the source

vo is the velocity of the observer

λ is the true wavelength

λ’ is the apparent wavelength

Key variables

Case 1:observer is in motion and the

source is at rest

f ’ = [ ( v ± vo ) / v ] f

( + ) means the observer is moving towards the source

( - ) means the observer is moving away from the source

Case 2:observer is at rest and the source

is in motion

f ’ = [ v / ( v ± vs ) ] f

( + ) means the source is moving away from the observer

( - ) means the source is moving towards the observer

Case 3:both the observer and the source

are in motion

f ’ = [ ( v ± vo ) / ( v ± vs ) ] f

NOTE: please refer to case 1 and case 2 and

analyze the situation of the observer and the

source respectively.

Conceptual understanding

When a wave source moves toward a receiver, does the

receiver encounter an increase in wave frequency, wave

speed ,or both?

Does the Doppler Effect occur for only some types of

waves or all types of waves?

Doppler Effect

change in wave frequency caused

by a moving wave source

moving toward you -

pitch sounds higher

moving away from you -

pitch sounds lower

named after Austrian physicist and philosopher Ernst Mach

Used to describe speed of objects that are travelling close

to, or above the speed of sound.

The ratio of the speed of the object and the speed of

sound in the medium.

M = speed of object / speed of sound

Shock waves

this is heard as a sonic boom when an airplane passes

over; this is the result of the compilation of sound waves

generated by a source that moves at equal or greater

velocity than the sound it creates

Sample problems:

Doppler effect

1. An ambulance traveling at 20. m/s sounds its siren at a frequency of 256Hz. What apparent frequency will you hear if the ambulance is:

( assume air temperature to be at 25°C )

a. approaching you?

b. moving away from you?

2. A car traveling at 30. m/s sounds its horn as it overtakes and pass another car traveling at 20. m/s in the same direction. If the frequency of the horn is 500. Hz, what is the frequency heard by the driver in the slower car:

a.) before

b.) after the car has passed?

Assume sound speed to be at 350. m/s.

LIST OF REFFERENCES This presentation is the combination of sources by the following:

Agatonlydelle. (2012). Physics Sounds. Online: http://www.slideshare.net/agatonlydelle/physics-sounds. Accessed online on: 06 march 2014

HMLSS21. (2012). Sound Waves BSU-ARASOF. http://www.slideshare.net/HMLSS21/sound-waves-bsuarasof. Accessed online on: 05 march 2014

Marium S. (2013). DAV Lecture: WAVE INTERACTIONS. Online: http://www.slideshare.net/saramarium1/sound-and-waves-26412647. Accessed online on: 05 march 2014

Moral F. (2014). Teacher at B.R.I.G.H.T. Academy: The Doppler effects. Online: http://www.slideshare.net/teacherfidel/16-the-doppler-effect?qid=c0a01b02-9c80-4a3c-861c-c18f4e6146e9&v=qf1&b=&from_search=2. Access online on: 05 march 2014