Sound

How Sounds Are MadeWhat happens when a bell shakes or a drum moves

up and down?

Vibrations occur – sound is produced when matter vibrates

Remember: sound travels as a longitudinal wave

Talking About SoundWhen you talk, air moves from your lungs

over your vocal cords, causing them to vibrate.

As your vocal cords move inward, the air between them is pushed together, creating a compression.

As your vocal cords move outward, less particles of air are left, creating a rarefaction.

Speed of SoundSpeed depends on the medium, NOT the

source.Speed of sound is determined by:

1. Temperature

2. Elasticity

3. Density

TemperatureLowering the temperature, makes the motion

of the particles more sluggish.The particles have a more difficult time of

moving and returning to their original positions.

Sound travels SLOWER at lower temperatures

and FASTER at higher temperatures.

Elasticity and DensitySound waves travel through any medium.

Native Americans use to put their ears to the ground to find out if buffalo were nearby. WHY?

Sound travels about 4 times faster in the ground than in the air.

Sound travels fastest in solids and slowest in gases.Think about walking in sand: you have to put in a lot

of energy to step. Sound is the same. In less-static mediums (like air or water), the waves travel slower.

Solids are usually more elastic.Would sound travel faster in water or air?

Elasticity and Density (Continued)Waves travel the FASTEST in solids and the

SLOWEST in gases.

GASES LIQUIDSSOLIDSair water leadHelium salt water

brickmilk

stone

Properties of SoundFrequency-number of waves that pass a

certain point in a certain amount of timeFrequency is measured in Hertz (Hz).

______________ Hz _________________ Hz

Frequency (continued)http://

www.youtube.com/watch?v=HpovwbPGEoo http://library.thinkquest.org/19537/java/Beats

.html

As the frequency increases, the number of waves increases.

Pitch – a description of a sound as high or low, which depends on the frequency of waves

Sound waves with a high-frequency have a high pitched sound, like a flute

A bass drum has a low frequency, so it produces a low pitch

Humans can hear sounds between 20-20,000 Hz.

Doppler Effect

http://www.youtube.com/watch?v=Kg9F5pN5tlI

http://www.lon-capa.org/~mmp/applist/doppler/d.htm

Doppler Effect (continued)Doppler Effect – change in sound or light that

occurs whenever there is motion between the source and its observer

The pitch of the siren is higher as it approaches you and lower when it moves away from you.

Intensity and LoudnessIntensityAmount of energy

carried by a wave in a certain amount of time

The larger the amplitude, the greater the intensity

Intensity is measured indecibels

InterferenceConstructive DestructiveWhen sound waves

combine to create a greater disturbance

When sound waves combine to make a wave that is less than either wave alone

Applications of SoundSonar Ultrasonic CleaningSonar: Sound Navigation And Ranging

Bats send out high-frequency sound waves, which bounce off objects and reflect back as echoes.

Bats use echoes to navigate or find their next meal.

Sonar is also used in commercial fishing, in cameras to focus, and in cars to warn of nearby objects.

Ultrasonic waves are used to clean jewelry, electronic components, and delicate machine parts.

Sound waves are sent through the liquid and the vibration knocks off the dirt.

Applications of Sound (continued)Sound and MedicineUltrasonic waves are

used to diagnose medical problems.Similar to sonar

Ultrasonic waves may be used to treat medical conditions by destroying unwanted tissue

How You Hear1. Sound waves enter the

outer ear, which acts as a funnel.

2. The waves move through the ear canal.

3. The waves hit a lightly stretched membrane called the eardrum. The eardrum vibrates.

4. The vibrations hid the middle ear, which consists of three small bones.

How You Hear (continued)5. The hammer, anvil,

and stirrup send the vibrations along.

6. The vibrations hit the liquid-filled inner ear.

7. The vibrations move to the snail-shaped cochlea.

8. The cochlea has hundreds of nerve fibers which convert the sound into an electrical impulse that is sent to the brain.