Sound & Hearing 17.4

Sound waves travel through a medium as energy is passed from particle to particle. If the particles are close together, as in a solid, the sound generally travels faster and less energy is lost.

Interest Grabber Can You Hear Through Your Desk? Listen carefully to the sound as you knock on your desk. Note how far your ear is from your hand when you make the sound. Without changing this distance, place your ear against your desk and knock again. 1.In each case, how did the sound travel to your ears? 2.What was the difference in the sound when you held your ear against the desk?

8L Sound words vibration pitch loudness sound amplify how high or low it sounds to the listener vibrations that can be heard to make sound louder how loud or quiet it sounds to the listener a backwards and forwards movement which transmits sound Match the words to the definitions.

2 second review Wavelength & Frequency -Wavelength is the distance between one part of a wave and the same part of the next wave -Frequency is the number of waves moving past a point in one second

The Facts Sound … 1. Is a form of energy produced & transmitted by vibrating matter 2. Travels in waves 3. Travels more quickly through solids than liquids or gases

Sound Waves -Alternating areas of high & low pressure in the air -ALL sound is carried through matter as sound waves -Sound waves move out in ALL directions from a vibrating object

What is sound? Sound is created by something vibrating. Imagine the surface of a drum. As the skin wobbles it pushes on the air next to it and squeezes it to make a little area of high pressure.

8L What is sound? Then the skin moves the other way and creates an area of low pressure. If this happens over and over again you get areas of high and low pressure being made. These areas pass through the air and to our ears where we detect them as sound.

Sound is a longitudinal wave -Where molecules are being pressed together as the sound waves move through matter JUST LIKE OUR SLINKY!!

8L Match signals to patterns of particles We can see these areas of high pressure with a microphone and an oscilloscope.

Pitch A measure of how high or low a sound is Pitch depends on the frequency of a sound wave For example, - Low pitch - Low frequency - Longer wavelength - High pitch - High frequency - Shorter wavelength

Sound Speed!!! How fast is the speed of sound? Depends what you are in!!!

8L Sound speeds Concorde was the first passenger jet to travel faster than the speed of sound. But how fast is that? The speed of sound: In air = 330 metres per second In water = 1500 metres per second In steel = 6000 metres per second Why did native American trackers put their ear to the ground if they wanted to listen for their prey?

Sound in Different Mediums

The Ear Sound is carried to our ears through vibrating air molecules. Our ears take in sound waves & turn them into signals that go to our brains. Sound waves move through 3 parts; outer ear, middle ear, & inner ear.

8L Hear this! Which parts can move? Which part carries a nerve signal? Which part is made of bone? ear flap (pinna) sound waves eardrum cochlea bones of middle ear nerves to brain

Sonar -An instrument that uses reflected sound waves to find underwater objects -For example, Animals use sonar or echo location to find their prey; these sounds have such a high pitch or frequency that the human ear cannot hear Humans use sonar to locate or map objects

8L Batty! Insect-eating bats use sounds with a frequency of Hz (or 80 kHz) to ‘see’ their prey. The bat sends out a sound and then listens for the echo as it bounces back from the insect. The bat compares the sound it hears from both ears to work out the direction the insect is in. What would happen to a bat if it went deaf in one ear?

8L Measuring loudness Why do we need a way to measure the loudness of sound? What unit is used to measure sound? I’ve asked you to turn that rubbish down! It’s too loud. You’ll damage your ears. It’s not as loud as you have the television. I’ve already turned it down – and it’s not rubbish!

8L Hear this!

The Doppler Effect The effect motion has on a sound. –When the sound is moving toward you the pitch increases because the wavelengths become compressed –When the sound is moving away from you the pitch decreases because the wavelengths become spread out Examples: –policepolice –TrainTrain –PlanePlane

Figure 18 The Doppler Effect

resonance The word resonance comes from Latin and means to "resound" - to sound out together with a loud sound. Resonance is a common cause of sound production in musical instruments.

8L The frequency range Make a list of these in order of frequency, starting with the lowest. AThe note middle C in the middle of a piano keyboard BBottom string on a bass guitar CTypical whistle for a dog DRumble from an earthquake EThe highest note sung by a human being DRumble from an earthquake BBottom string on a bass guitar AThe note middle C in the middle of a piano keyboard EThe highest note sung by a human being CTypical whistle for a dog

1. I can increase the pitch of a note on a guitar by... a) plucking the string harder b) tightening the string c)holding the guitar tighter. 2. I play the lowest notes on an electric guitar by... a) not pressing on the strings on the fretboard b) touching the strings very gently c) turning the volume down on the amplifier. 8L Rock legends?

3. Hitting the strings hard on a guitar will... a) make the note louder b) make the note higher pitched c)hurt my fingers. 4. The sound from an electric guitar dies away when... a)the string stops moving b) the guitarist stops plucking the strings c) the strings are magnetised. 8L Rock legends?

5. A drummer can change the pitch of the drum by... a) changing the tightness of the drum skin b) hitting the skin harder c)using different drumsticks. 6. A drummer grabs hold of a vibrating cymbal to... a) stop it making a sound b) change the pitch of the sound c) stop it falling off the stage. 8L Rock legends?

That’s all folks!