Sound
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Sound • Acoustics is the study of sound. • All sounds are waves produced by vibrating objects - tuning forks, vocal chords, reeds, lips, columns of air, strings, cricket legs • Demo – tuning forks - water
Sound
Sound Waves • Sound is a longitudinal wave with compressions and rarefactions. • Q- Draw a sound wave. Label areas of high pressure and low pressure.
Sound Waves • Notice that the air molecules move in a direction parallel to the direction of the wave. • Demo – Slinky on the floor.
Speed of Sound • The speed of propagation Medium Air
Speed of sound 343 m/s
Steel
5100 m/s
Water
1370 m/s
Vacuum
0 m/s
Speed of Sound vs Snowball
http://teachers.springisd.org/craigm/sup
Speed vs Temp • As temperature increases, the speed increases. 0.6 m/s per *C
Speed of Sound vs Speed of Light Sound = 343 m/s Light = 300, 000, 000 m/s Notice that light travels much faster.
Lightning & Thunder • Light reaches you in an extremely short period of time. • Sound reaches you at a much slower rate. It takes about 5 seconds to travel 1 mile.
The delayed sound reaching your ear after the light. • Other examples include – starters pistol, chopping wood • You see the event(light), count the number of seconds until the sound arrives. 5 seconds = 1 mile 10 seconds = 2 miles
Pitch • The pitch is determined by the frequency of the sound. Units are Hz or vibrations per sec. • Humans hear 20 to 20,000 Hz
• Loud noises can damage your hearing. This usually lowers your upper limit. The tiny hairs in the inner ear may fall out.
Path that sound travels • • • • • •
Sequence of vibrations from the source To the ear drum To the bones in the middle ear To the fluid in the inner ear To the hairs in the inner ear To the nerves which go to the brain on the auditory nerve.
Musical Notes • • • •
A B C D E F G A etc Low C is 256 Hz Middle C is 512 Hz High C is 1024 Hz
• Notice that each octave is double the frequency.
What is it that vibrates? • • • •
Demo – Straws Demo – Happy BD Box Demo – Water in glasses Demo – Oscilloscopes and tuning forks and voices
Loudness of Sound • How loud a sound seems is determined by the waves amplitude. This is proportional to its energy. • For an increase in 10 dB, the energy is ten times greater.
Loudness Sound
Decibels
Hearing threshold Rustle of leaves
0
Conversation Rock Concert Pain Threshold Jet Engine
10 60 110 120 130
Reflection of Sound • Reflection of sound is called an echo. • Sound waves reflect off of hard smooth surfaces. • Curtains and rugs results in most of the sound being absorbed (transmitted).
Interference of Sound Waves • Constructive Interference
Doppler Effect • Breaking the sound barrier
Sound
Sound Waves • Sound is a longitudinal wave with compressions and rarefactions. • Q- Draw a sound wave. Label areas of high pressure and low pressure.
Sound Waves • Notice that the air molecules move in a direction parallel to the direction of the wave. • Demo – Slinky on the floor.
Speed of Sound • The speed of propagation Medium Air
Speed of sound 343 m/s
Steel
5100 m/s
Water
1370 m/s
Vacuum
0 m/s
Speed of Sound vs Snowball
http://teachers.springisd.org/craigm/sup
Speed vs Temp • As temperature increases, the speed increases. 0.6 m/s per *C
Speed of Sound vs Speed of Light Sound = 343 m/s Light = 300, 000, 000 m/s Notice that light travels much faster.
Lightning & Thunder • Light reaches you in an extremely short period of time. • Sound reaches you at a much slower rate. It takes about 5 seconds to travel 1 mile.
The delayed sound reaching your ear after the light. • Other examples include – starters pistol, chopping wood • You see the event(light), count the number of seconds until the sound arrives. 5 seconds = 1 mile 10 seconds = 2 miles
Pitch • The pitch is determined by the frequency of the sound. Units are Hz or vibrations per sec. • Humans hear 20 to 20,000 Hz
• Loud noises can damage your hearing. This usually lowers your upper limit. The tiny hairs in the inner ear may fall out.
Path that sound travels • • • • • •
Sequence of vibrations from the source To the ear drum To the bones in the middle ear To the fluid in the inner ear To the hairs in the inner ear To the nerves which go to the brain on the auditory nerve.
Musical Notes • • • •
A B C D E F G A etc Low C is 256 Hz Middle C is 512 Hz High C is 1024 Hz
• Notice that each octave is double the frequency.
What is it that vibrates? • • • •
Demo – Straws Demo – Happy BD Box Demo – Water in glasses Demo – Oscilloscopes and tuning forks and voices
Loudness of Sound • How loud a sound seems is determined by the waves amplitude. This is proportional to its energy. • For an increase in 10 dB, the energy is ten times greater.
Loudness Sound
Decibels
Hearing threshold Rustle of leaves
0
Conversation Rock Concert Pain Threshold Jet Engine
10 60 110 120 130
Reflection of Sound • Reflection of sound is called an echo. • Sound waves reflect off of hard smooth surfaces. • Curtains and rugs results in most of the sound being absorbed (transmitted).
Interference of Sound Waves • Constructive Interference
Doppler Effect • Breaking the sound barrier
