sound and waves grade 6 pps
TRANSCRIPT
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Sound
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Overview
•The Facts of Sound•Sound Vocabulary•The Ear and Sound
•Musical Instruments and other uses of Sound
•Other types of waves
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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
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Sound waves travel faster through solids because there are more particles close together to transfer the energy.
Sound waves and
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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
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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.
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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
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Sound Waves
- Alternating areas of high and low pressure in the air (compressions and rarefactions)
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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)
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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)
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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)
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Compression
Where particles are pressed
together as the sound wave
moves through matter.
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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
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• Compressions - The close together part of the wave.• Rarefactions - The spread-out parts of a wave.
Compression Wave = Longitudinal Wave
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Longitudinal Wave (Compression Wave)
Each wave particle vibrates back and forth in the same direction of the wave.
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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 ….
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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.
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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
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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
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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
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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
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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
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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
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The Human Ear
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Amplitude
is the maximum distance
the particles in a wave
vibrate from their rest positions.
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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
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Amplitude = loudness
•The volume or loudness of sound is measured in decibels
dB
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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
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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
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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.
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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
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Ultrasound (above 20,000 Hz)
Ultrasound waves are used in medicine They are also reflected sound waves
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Other types of waves
• Remember sound waves are longitudinal and mechanical
•Other waves are transverse, electromagnetic and water waves
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Transverse waveswave particles vibrate
in an up-and-down motion.
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Transverse waves
• Crests - Highest part of a wave• Troughs - The low points of the
wave
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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
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Water Waves
• The blue surface particles move in a clock-wise direction
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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
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That’s all folks!