Waves

1
Unit 10

• Waves Wave Properties
• Sound Waves

2
Sound Waves

• Waves caused by disturbing a medium results in
  noise, music, vibrations you cant hear by
  other animals can.
• Mechanical Waves
• Need a medium (solid, liquid, gas) to travel
• Longitudinal Waves
• Vibrations are parallel to wave motion.

3
Sound Waves

• Sound waves need a medium to travel
• If the medium changes, the speed of sound
  changes.
• Average Speed of Sound Air 340m/s
• Sound moves the fastest through solids
• and the slowest through gases.
• solids ? liquids ? gases
• Sound moves the fastest through hot air and the
  slowest through cold air.
• hot air ? cold air

4
Sound Waves

• Notice the frequency and wavelength DO NOT change
  the speed of sound.
• Changing the frequency changes the wavelength.
• Changing the wavelength changes the frequency.
• A high frequency means it is high pitch (alto
  singer)
• A low frequency means a low pitch (baritone
  singer)
• There are sounds people cannot hear.
• Ultrasonic sounds are pitches higher than human
  hearing.
• higher than 20,000 Hz
• Infrasonic sounds are pitches lower than human
  hearing.
• lower than 20Hz

f
?
?
f
5
Sound Waves

• You can change the loudness of a sound two ways.
• Change the amplitude (amplify)
• You can amplify a wave by turning up the
  volume, OR by adding to the wave again and again
  ... And again and again
• Turning up the volume is increasing the
  decibel level of the source.
• Everything is vibrating (every object vibrates,
  natural frequency) you can amplify the wave
  if you match its natural frequency.
• Change the intensity
• Intensity can be changed by your
• distance from the source.
• The closer you are to the source,
• the more intense the sound, aka louder

6
If a tree falls in the forest and no one is
around to hear it does it still make a sound?
7
If a tree falls in the forest and no one is
around to hear it does it still make a sound?

• Yes! A sound wave is a sound wave whether or
  not you can hear it.
• Sound waves are a vibration. A disturbance of
  molecules!
• There are many sounds people cannot hear but
  they are still sounds!
• If a tree falls it disturbs the molecules in
  the air and the ground, therefore creating a
  wave! It makes a sound!

8
If a tree falls in the forest and no one is
around to hear it does it still make a sound?

• Normal hearing frequencies range from 20 Hz
  20,000Hz
• Frequencies higher than 20,000 Hz (Ultrasonic)
  and lower than 20Hz (Infrasonic) are out of
  normal human range.
• The older you get the smaller your range of
  audible sounds gets! Old people have a lot of
  trouble hearing high frequencies (high pitch
  voices)
• Which is why Grandma cant understand you little
  sister as well as she can understand you!

9
Old People Hearing Sounds - Frequency
Jump to the time 130 for the action! For
HopeHSBlueWave.org website use Video can be
found in Video page title Old People
Hearing Sounds

• Check out these old teachers listening to sound
  waves as they go higher and higher in frequency.
  
• The teachers will put their hands down when they
  can no longer hear the sound.
• Who will put their hand down first?
• (Note The camera actually doesnt pick up the
  sound after a certain frequency, so dont worry
  if you cant hear it in the video
• in class we did the same experiment)

10
People Hearing Sounds Intensity
11
Both Intensity and Frequency
Frequency (Hz)
12
Infrasonic and Ultrasonic Waves

• Dog whistles are high pitched so that dogs can
  hear them, but not humans.
• Dolphins and bats use sonar aka ultrasonic
  waves to communicate and see barriers.
• We have imitated them and use ultrasonic waves
  for ultrasounds!
• Whales, elephants, hippos, and other animals use
  infrasound to communicate over distanceswhales
  can do this over the distance of hundreds of
  miles!
• Infrasonic waves can be used to predict natural
  disasters such as tornados, volcanic eruptions,
  etc.

13
Doppler Effect Sound WavesWhy does each
observer hear a different sound?
This is the Doppler Effect! Each observer hears a
different sound because as the motorcycle moves,
it catches up with its own sound waves.
Observer B hears a high frequency because the
waves are closer together (small wavelength).
Observer A hears a low frequency because the
waves are farther apart!
14
The Doppler effect makes sources of sound appear
to be higher and lower pitch based on their
relative motion.
Doppler Effect Sound Waves
Moving towards the observer higher frequency
Moving away from the observer lower frequency
Low frequency means low pitch!
High frequency means high pitch!
15
Por ejemplo
For HopeHSBlueWave.org website use Video can be
found in Video page title Doppler Effect
002 and Doppler Effect 003
Doppler Effect Sound Waves
You can actually close your eyes and tell when
the car has gone by you. There is a very
distinct high to low pitch (frequency)
change as the car just passes the camera. Dont
confuse this with loudness in the moment right
before the car passes you and the moment right
after the car passes you it would be the same
distance from you. But the distinct difference
in sound you can hear is the difference in
frequency, high and low pitch due to the car
moving towards you or away from you.
16
http//www.youtube.com/watch?vTn35SB1_NYI
Doppler Effect Sound Waves
http//youtu.be/h4OnBYrbCjY (1-2min)
17
FREQUENCY IS NOT LOUDNESS!
and remember
Frequency is pitch high or low pitch not
LOUD!

• Its not FLIPPING louder if it is more frequent!

18
Superposition Principal Sound Video of Beats

• http//www.acoustics.salford.ac.uk/feschools/waves
  /super3.htm

19
Reflection SoundSound waves reflect off of
boundary (object) if they are the same size or
smaller than the boundary.
Ultrasonic waves are high frequency and low
wavelength. Since they have a small wavelength,
they can reflect off more barriers, so the
dolphin or ultrasound can see more objects.
For Sound Waves - reflection only happens when
the sound wave is the same size or SMALLER than
the boundary! Big waves would miss things! ?
20
Reflection SoundEcholocation

• Bats and dolphins use echolocation to see.
• They send out ultrasonic waves and when they are
  reflected off a boundary the bats and dolphins
  can not only see there is an object and its
  relative size but also if it is stationary,
  moving towards them or away from them!
• The Doppler Effect will change the frequency of
  the returning wave based on its motion!

21
Resonance and Forced Vibrations

• Resonance is when the frequency of a force
  applied matches the natural frequency of
  vibration of an object and causes an increase in
  the waves amplitude.

These are all examples of mechanical waves being
amplified due to resonance.