Sound

Overview

•The Facts of Sound•Sound Vocabulary•The Ear and Sound

•Musical Instruments and other uses of Sound

•Other types of waves

The Facts

Sound …1.… is a form of energy produced &

transmitted by vibrating matter

2.… travels in longitudinal waves

3.…travels faster through solids than liquids or gases

Sound waves travel faster through solids because there are more particles close together to transfer the energy.

Sound waves and

Speed of Sound• Medium (Matter) Speed

m/sec gas air (0

o C) 331

air (20o C) 343

water (25o C)

1493

liquid sea water 1533 iron 5130

copper 3560 solid glass 5640 diamond 12000

Vibration

- Very fast, repeated backward and forward movement of particles of matter

- For example, the vibration of the tuning fork creates pure sound.

- The hammer hits the nail and the particles vibrate making noise.

Watch the 3 red dots

You will see them vibrate, but not move with the wave to the end.

All the particles are vibrating but stay fixed

Waves transport energy without moving matter

Sound Waves

- Alternating areas of high and low pressure in the air (compressions and rarefactions)

Sound Waves

- ALL sound is carried through matter as sound waves. In a vacuum there are no particles so sound cannot travel.

- Alternating areas of high and low pressure in the air (compressions and rarefactions)

Sound Waves

- Because sound waves need particles to be transmitted they are mechanical waves

- ALL sound is carried through matter as sound waves. In a vacuum there are no particles so sound cannot travel.

- Alternating areas of high and low pressure in the air (compressions and rarefactions)

Sound Waves

- Sound waves move out in ALL directions from a vibrating object.

- Because sound waves need particles to be transmitted they are mechanical waves

- ALL sound is carried through matter as sound waves. In a vacuum there are no particles so sound cannot travel.

- Alternating areas of high and low pressure in the air (compressions and rarefactions)

Compression

Where particles are pressed

together as the sound wave

moves through matter.

Compression- Where particles are pressed together as

the sound waves move through matter- For example,

- a wave travels through the springs just like sound waves travel through the air

- the places where the springs are close together are like compressions in the air.

compression

• Compressions - The close together part of the wave.• Rarefactions - The spread-out parts of a wave.

Compression Wave = Longitudinal Wave

Longitudinal Wave (Compression Wave)

Each wave particle vibrates back and forth in the same direction of the wave.

Sound waves covered till now:

• States of matter (solid, liquid, gas)• Speed of sound through matter• No sound in a vacuum• Vibration• Compression + Rarefaction• Longitudinal waves

•Remember that ….

Frequency= waves/time

If you watch the 3 red dots you will see them vibrate, but not move with the wave to the end.

Waves transfer energy without moving matter.

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 passing a point in a certain tme

- Many waves = high frequency- Few waves = low frequency

Pitch = Frequency

• 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

Frequency is measured in Hertz

• For example:

If 20 waves are made per second, then the frequency is 20 cycles per second =

20 Hertz

• Hz

20 Hz – 20,000 Hz

The human ear can only hear sounds between

20Hz and 20,000 Hz (Frequency/Pitch)

Below 20 Hz is called infrasound

Above 20,000 Hz is called ultrasound

Ultrasound

sound waves with frequencies above the normal human range of hearing. Sounds in the range from 20,000-100,000Hz

Infrasound sounds waves with frequencies below the normal human range of hearing.Sounds in the 0.001 - 20Hz range

The Ear• Sounds reach our ears through

vibrating air particles• Our ears capture sound waves and turn

them into signals that go to our brains• Sound waves move through 3 parts of

the ear; outer ear, middle ear, + inner ear

The Human Ear

Amplitude

is the maximum distance

the particles in a wave

vibrate from their rest positions.

Amplitude = loudness

• The intensity of a sound decreases as you move away from a sound. The sound is softer.

• As the source of a sound comes closer the sound becomes louder, more intense

• A loud sound has a high amplitude

• A soft sound has low amplitude

soft

loud

Amplitude = loudness

•The volume or loudness of sound is measured in decibels

dB

Loudness of Sound in Decibels

Sound Loudness (dbs) Hearing Damage

Average Home 40-50

Loud Music 90-100 After long exposure

Rock Concert 115-120 Progressive

Jet Engine 120-170 Pain

Sound and Instruments- Different musical instruments create

different sound vibrations

- Wind instruments by blowing and vibrating the air e.g. flute, saxophone, organ

- String instruments by touching and vibrating the strings e.g. guitar, violin, piano

- Percussion instruments by hitting a surface e.g. drums, cymbals, triangle

Sound and Instruments- Instruments can be played at different

pitches (musical notes) by changing the lengths of different parts.

- For example,

- Another way to make different pitches is to change the thickness of the material that vibrates.

A trombone’s mute absorbs some of the

sound waves produced, so a different sound is made.

Sonar

- Sonar uses reflected sound waves (echoes) to find objects in water or air

Animals use sonar or echo location to find their prey (food); these sounds have such a high pitch or frequency that the human ear cannot hear them

Humans use sonar to locate or

find objects

Ultrasound (above 20,000 Hz)

Ultrasound waves are used in medicine They are also reflected sound waves

Other types of waves

• Remember sound waves are longitudinal and mechanical

•Other waves are transverse, electromagnetic and water waves

Transverse waveswave particles vibrate

in an up-and-down motion.

Transverse waves

• Crests - Highest part of a wave• Troughs - The low points of the

wave

Electromagnetic waves• Electromagnetic waves travel as

transverse waves

• Electromagnetic waves CAN travel through a vacuum

• Light, microwaves, x-rays, and TV and radio transmissions are all examples of electromagnetic waves

Water Waves

• The blue surface particles move in a clock-wise direction

Wave concepts covered in this power point:

Sound Waves• States of matter (solid, liquid,

gas)

• Speed of sound through matter• No sound in a vacuum• Vibration• Compression + Rarefaction• Longitudinal waves• Wavelength• Frequency = Pitch• Hertz Hz• 20 – 20,000 Hz • Ear (outer, middle, inner ear)

• Amplitude = Loudness = Volume

• Decibels dB• Sonar• Ultrasound, infrasound

Other waves

• Transverse waves• Crests• Troughs• Electromagnetic

waves• Water waves

That’s all folks!