Chapter 10 Sound

Sounds are caused by waves Longitudinal Waves The direction of the wave is also the direction of the particle movement Travels through air It is a mechanical wave Needs matter to travel through Energy is transferred when one particle collides with another In the compression part of the wave, the particles are pushed close together In the rarefaction part, the particles are further apart

Mediums Sound can travel through any medium Air is the most obvious In water, sound travels faster but is less clear In solids, sound travels even faster Recall that the different forms of matter have properties based on how the atoms are arranged

Where can’t sound be transmitted? In the absence of matter, sound waves can not transfer energy. This means that, in space, there can be no sound Astronauts must use transmission equipment to talk to, and hear one another

Speed of Sound Sound travels at different speeds in different mediums Air, liquids, solids It also travels different speeds through each medium depending on the temperature, density, and elasticity of the matter

Temperature As the temperature of any matter increases the particles in the matter move faster. More collisions=more energy transfer=more heat This increase in collisions also affects the transfer of sound waves If particles are moving faster, they are bumping into each other more, and therefore transferring sound faster If the matter is cooled, the particles move slower and sound is slower to transfer. The speed of sound in air at room temperature (21 degrees C) is 346m/s At 0 degrees C, the speed falls to 330 m/s

Density Density=mass/volume If the particles in an object are closer together, the object will be more dense In a dense object, particles bump into one another more often This will transfer energy (sound) more quickly

Elasticity Elasticity-the tendency of an object to rebound to its original state when deformed Rubber bands have high elasticity Paper does not (It stays deformed) Sound waves travel more quickly through elastic objects Solids tend to be more elastic (air and liquids do not stretch)

How do we hear sound? Human ears have the ability to collect sound waves and transfer signals to the brain The brain reads the signals There are 3 sections of the ear The outer ear The middle ear The inner ear

The outer ear The part that you see (cartilage) along with the ear canal and ear drum The shape of the ear helps gather sound waves and direct them into the ear canal. The ear canal is 2-3cm long, and about 0.7 cm in diameter The sound waves travel down this canal until they reach the ear drum The ear drum (a.k.a. Tympanic membrane) is a tough membrane that vibrates when sound waves reach it It is about 0.1 mm thick

Middle Ear As the Tympanic Membrane vibrates, it passes the sound waves into the middle ear Consists of 3 bones Malleus (hammer) Incus (Anvil) Stapes (Stirrup) As these bones vibrate, they amplify the sound waves The Stapes is connected to the oval window, and causes it to vibrate

The inner ear Fluid-filled portion of the ear The oval window fibrates, transferring the sound waves to fluid waves that travel through the inner ear The inner ear contains the cochlea Filled with fluid and contains tiny hair cells, which transmit signals to the auditory nerve (cochlear nerve), through which they travel to the brain The brain reads the signals and deciphers them

Hearing loss Damage to the ears can result in hearing loss Loud noises can damage or destroy the hair cells in the cochlea These do not grow back and cannot be replaced Research is looking into ways to fix this The easiest way to avoid hearing loss is to refrain from loud music