Sound waves are caused by vibrations and carry energy through a
medium Sound Demonstrations
Slide 2
What is a sound wave? BrainPop password and login mcbrayer
BrainPop
Slide 3
Humans hear sounds waves in a limited frequency range From 20
vibrations per second (20 Hertz) to 20,000 vibrations per second
(20,000 Hertz) The number of vibrations that are produced per
second is called frequency. Frequency varies for each sound and is
measured in hertz. One hertz is equal to one vibration per
second.
Slide 4
How does frequency affect pitch? A sound with a low frequency
will have a low pitch, such as a human's heartbeat. A sound with a
high frequency will have a high pitch, such as a dog whistle.
Sounds below the range of human hearing is Infrasound. Sounds with
a frequency above the range of human hearing is Ultrasound.
Slide 5
How do we measure sound? Sound meter and oscilloscope (A device
for viewing oscillations, as an electrical voltage or current, by a
display on the screen.) Use Microphone and applets on computer.
Test Your Hearing range It is best to use headphones and be in a
quiet room. Test Your Hearing range
Slide 6
How will your hearing range change? The hearing range of humans
gets worse with age. People lose the ability to hear sounds of high
frequency as they get older. The highest frequency that a normal
middle-aged adult can hear is only 12-14 kilohertz. Also, the
hearing range for men worsens more quickly than the hearing range
for women. This means that women will have the ability to hear
notes of higher pitch than men of the same age do.
Slide 7
Slide 8
Loudness is measured in decibels (dB) Amplitude = Loudness We
hear pressure (the amplitude) of sound as loudness. It takes more
energy to create a louder sound. Too loud of a sound can cause
deafness.
Slide 9
Amplitude The bigger the difference in the amplitude of the
wave the louder the sound.
Slide 10
Pitch a measure of how high or low a sound is and depends on
frequency Penny Whistle - show how works. Homemade Penny whistle
(need straws and scissors) Make and then cut to change pitch Make
and add a hole at the end How is the sound made? Have you ever held
a blade of grass between you thumbs and made it sing? How does
cupping your hands around the blade help the sound? Boom Wackers
Without the cap Whack two different tubes against your upper leg.
Compare tubes of different lengths. Which tube produced a lower
tone? Why do you think the longer tubes produced lower tones? Cap
one end of the tube and whack again. How does the tone of the caped
tube compare to the open tube? Strike a 288 Hz tuning fork and hold
it just on the inside end of the tube How does wavelength affect
pitch? The longer the wavelength the lower the pitch.
Slide 11
Mechanical waves need a medium Clock in a vacuum Medium affects
the speed of the wave Oven racks (vibrations, pitch and frequency)
Can telephone
Slide 12
Speed of sound In Air (0 degrees C) = 331 m/s In Air (100
degrees C) = 386 m/s Oxygen = (0 degrees C) = 317 m/s In Water =
1,490 m/s Copper = 3,813 m/s Rubber = 54 m/s
Slide 13
Tuning forks Tuning forks touch to water in glass, touch to
different materials how does that affect the sound/vibrations? The
wavelength of the sound that the tuning fork emits is much larger
than the width of the tuning forks tines. As a result, air has
plenty of time to move around the tines during each cycle of
vibration. Thus, instead of pushing air toward and away from your
ear as it vibrates, each tine prevents the air from flowing around
it and helps the tine push the air toward and away from your ear.
You hear much more sound as a result.
Slide 14
Slide 15
Waves and Vibrations Thunder Drum- The vibrating spring causes
the drumhead to vibrate, which in turn causes the air inside the
drum to vibrate. The air in the drum begins to resonate, and the
volume of the sound increases. Resonance a phenomenon that occurs
when two objects naturally vibrate at the same frequency. For
example, when both the guitar body and the string are vibrating at
the same frequency. The guitar body has a larger area than the
string and is in contact with more molecules in the air. So the
body is a better at transferring the vibrations to the air than the
string is. Breaking of a wine glass Tacoma Bridge collapse How does
this relate to the Thunder Drum?
Slide 16
Waves and Vibrations The natural frequency of an object depends
on the objects shape, size, mass, and the material from which the
object is made Talking Cups Telephone cans How is sound transferred
from one can to the other? What is the medium that it is being
transferred in? Sound waves are what type of wave? Wine glasses
with water Your finger slides and sticks. Bowing the wineglass much
the same way a violinist bows a violin string. With each cycle of
vibration you add a bit of energy. Which glass has the highest
pitch? Did it have more or less water in it? What do you believe
caused the sound, the water, the air, or the glass? How could you
set up a musical scale?
Slide 17
Waves and Vibrations Glass bottles with water (Jacob) Gently
strike the side of the bottle with a metal spoon. Please note which
bottle has the highest pitch and which has the lowest. What
vibrated to make the sound you heard? Where did you hit the jar to
give the best sound? What is your hypothesis which bottle will have
a higher pitch and which will have a lower pitch. What did you find
out?
Slide 18
Natural frequency Singing Rod Just like the wine glasses,
guitar, singing cups, thunder drum the singing rod has a natural
frequency its particles want to vibrate at when energy is
introduced. By holding the rod at the node (the place where the
object is not moving) and vibrating the antinode the natural
frequencies of vibration can be achieved. Touching a node will not
dampen the sound; touching an antinode will.
Slide 19
Harmonic Vibrations Plastic swing tube Twirl above head
Increase the speed of the tube Change the direction you spin the
tube Change the end of the tube you are holding and do all of the
above steps again. Choose the end that worked the best and try
lifting the tube up and down when you spin it What did it sound
like? What type of sound did it make? Did the sound change when you
increased the speed? What did it sound like? Did changing the
direction change the sound? Did changing the direction of the tube
change the sound? Write a statement explaining how best to get
sound from the tubes. How does the speed of the tube affect pitch?
The air a the tube ends flows inward and outward together and the
air at the middle of the tube experiences up and down pressure
fluctuations, but no velocity fluctuations. The higher the tones
the more places in the tube that are experiencing up and down
pressure fluctuations.
Slide 20
Standing Waves Carpet Tubes What happens to the air in the tube
as it is lowered over the flame? What happens to the pitch when the
size of the tube changes? This is really the principle used by any
wind instruments in a band or orchestra. The instrument has a
hollow tube of some sort, its length will determine which
frequencies it will amplify and its shape will determine the
quality or type of sound it will give out. The musician produces a
vibration, usually with the lips or a reed, and the air in the
hollow tube will vibrate in resonance with whatever frequency it is
designed to amplify.
Slide 21
Standing Wave Guitar or Violin String Pressing down on the
string creates a node at that point. The location of the node
determines the pitch of the note.
Slide 22
Interference When several waves are in the same location, they
combine to produce a single, new wave that is different from the
original wave. Constructive Interference increases the amplitude.
Destructive interference decreases amplitude.
Slide 23
Tuning forks Strike the prongs of a large tuning fork with your
rubber heal. Observe the loudness of the sound and use a stopwatch
to measure the length of time it can be heard before it dies away.
What was the relative loudness of the tuning fork, was it loud or
could you barely hear it? How long does it take for the sound to
die out so you can no longer hear the tuning fork? Strike the fork
again. This time hold the rod end firmly against a tabletop.
Observe the loudness of the sound and time the length of time it
can be heard. What is the relative loudness now, was it loud or
could you barely hear it? How long does it take for the sound to
die out so you can no longer hear the tuning fork? What happens
when the tuning fork is placed near water? Which would spill the
water the most a small tuning fork or a large tuning fork?
Why?
Slide 24
Gas Bottles with water and Tuning Fork Each time the tuning
fork is held above the glass bottles you are actually hearing 2
sounds, not one. You are hearing the sound made by the tuning fork
and the sound that reflects off the water and reemerges from the
jar. When the reflected wave reemerges, it overlaps with the wave
coming from the tuning fork. If the wave emerging from the jar
overlaps constructively you will hear a loud sound. If the emerging
wave overlaps destructively, you will hear no sound or a very low
amplitude sound. How does this demo also relate to Resonance?
Slide 25
Doppler Effect Motion between the source of waves and the
observer creates a change in observed frequency. Frequency changes
the Pitch Examples Ambulance Doppler ball Doppler Radar Radar dome
receives radio waves that have been sent out an then reflected back
by rain, snow, and hail. Meterorologist observe frequency shifts.
Do you remember learning about the Doppler Shift in space
science?