Properties of a Wave

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Properties of a Wave
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Waves have properties

• Just like different substances have different
  properties
• Example Hydrogen is a gas but Silver is a solid
  at room temperature
• Example Water has a freezing point, a boiling
  point, etc

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Wave Speed

• The speed of a wave depends on the properties of
  the medium in which it travels.
• THIS IS A PROPERTY OF THE MEDIUM NOT THE WAVE
  (LIKE BOILING POINT, DENSITY, ETC)
• The speed of a wave does not depend on the
  amplitude or frequency.

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Examples

• Solids, liquids and gases are different mediums.
  The same wave will travel through each medium
  differently.
• WHY?
• Solids have molecules that are tightly packed.
• This is why sound is distorted in water the
  sound waves travel through a different medium
  than air.

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Watch this!

• http//study.com/academy/lesson/what-is-sound-defi
  nition-wave-parameters-pitch-volume.html
• https//www.khanacademy.org/test-prep/mcat/physica
  l-processes/sound/v/relative-speed-of-sound-in-sol
  ids-liquids-and-gases

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What does the speed of a wave depend on?

• Solids are more tightly packed because of strong
  interactive forces so waves travel faster in
  solids than liquids and faster in liquids than in
  solids
• The mass of the particles of the medium (the
  greater the mass/inertia of the particles, the
  SLOWER the wave moves)
• Density of material
• More dense means slower speed
• However, the material can also absorb sound
  instead of passing it on

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Summary

• Waves have properties that depend on the material
  the wave is traveling in
• Speed is affected by the MEDIUM not the amplitude
  or frequency
• Same material same speed
• I REPEAT Same material same speed
• Waves travel faster in solids than in liquids
• Waves travel faster in liquids than in gases
• Higher mass/density/inertia slower speed
• This is why sound waves are distorted in water
• Some materials also ABSORB energy

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Amplitude and Energy

• The amplitude tells us how much energy is
  transferred
• This is why loud sounds are shown with larger
  waves
• Although a wave with a larger amplitude transfers
  more energy, it moves with the same speed as a
  smaller amplitude wave through a given medium.
• As long as the material is the same, the speed is
  the same.
• Watch this https//www.youtube.com/watch?vDztZD
  NDUaiQ

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Frequency vs Amplitude

• Frequency is how many cycles of a wave occur in 1
  second
• Amplitude is the height of the wave
• Amp and Frequency are not the same!!!
• Frequency does not change if the medium changes

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Summary of the Amplitude, Frequency, and Speed

• Energy transferred depends on the AMPLITUDE
  (larger amp more energy)
• Frequency is how many cycles of a wave occur in 1
  second
• Frequency, amplitude, and speed are not the same!
• Frequency of a wave does not change if the medium
  changes but speed and amplitude will
• Wavelength, frequency, amplitude do not affect
  speed of waves only the medium does!

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Quick Quiz

• 1. A teacher attaches a slinky to the wall and
  begins introducing pulses with different
  amplitudes. Which of the two pulses (A or B)
  below will travel from the hand to the wall in
  the least amount of time? Justify your answer.

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Answer

• Both arrive at the same time!
• Same material!

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• 2. Which of the two pulses (C or D) will travel
  faster from the hand to the wall? Justify your
  answer.

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Answer

• Neither!
• Both will have the same speed. Since they go the
  same distance they will arrive at the same time!

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• 3. Two waves are traveling through the same
  container of nitrogen gas. Wave A has a
  wavelength of 1.5 m. Wave B has a wavelength of
  4.5 m. The speed of wave B must be ________ the
  speed of wave A.
• a. one-ninth
• b. one-third
• c. the same as
• d. three times larger than

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Answer

• C.

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• 4. The speed of a wave depends upon (i.e., is
  causally affected by) ...
• the properties of the medium through which the
  wave travels
• the wavelength of the wave.
• c. the frequency of the wave.
• d. both the wavelength and the frequency of the
  wave.

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Answer

• A

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Natural Frequency

• A pendulum or spring (wave) has a natural
  frequency the speed at which it vibrates
  freely.
• Everything has a natural frequency bridges,
  buildings, etc
• The frequency depends on the length and tension
  of the medium . Shorter springs and pendulums
  have higher natural frequencies than longer ones.
  
• Example Guitar Strings we shorten the strings
  to change the note (ie the frequency that the
  string vibrates naturally)
• To tune a guitar we tighten the strings or loosen
  them to get them to vibrate at the correct
  frequency (note).

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Resonance

• Phenomena that occurs when energy is added to a
  vibrating system at the same frequency as its
  natural frequency.
• Resonance makes the amplitude of the vibrations
  become larger.
• The waves interact with each other and add
  together.
• Example When you push someone on a swing or use
  their legs to push at the same frequency (at the
  natural frequency) they will go higher! This is
  because energy is added at the natural frequency.
  

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Resonance Examples

• Bay of Fundy Tides https//www.youtube.com/watch?
  vlha-yk-rgq0
• When a choir sings
• Shattering of glass
• https//www.youtube.com/watch?vBE827gwnnk4
• Allows us to pick up TV/radio signals (electrical
  resonance)
• MRIs Magnetic Resonance Imaging (magnetic field
  allows doctors to look inside you!)
• http//www.youtube.com/watch?vH0adTNhzGxU
• Your car going at a certain speed starts to
  vibrate! (poor wheel alignment)
• Tacoma Narrows Bridge (video from before!) wind
  was IN PHASE with natural frequency of bridge

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Resonance

• https//www.youtube.com/watch?vC-Bn70PpbrM
• 545 watch a few minutes here (the experiment)
• 11 min watch this experiment

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Summary

• Natural Frequency the speed at which something
  vibrates at naturally. It depends on properties
  of the medium (length, tension).
• Ex Guitar strings have a natural frequency that
  corresponds to a note.
• Resonance - Phenomena that occurs when energy is
  added to a vibrating system at the same frequency
  as its natural frequency. Amplitude (and energy)
  increases.
• Ex Using your legs on a swingset to go higher.

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Questions for You

• 1) Which substance would a wave travel faster in
  and why? A) Ice cube or water?
• B) Jello before it is set or after it is
  set?
• c) Steam or water?
• Orange juice or water?
• Body fat or bone?
• Bone or muscle?

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• 2) Explain what the natural frequency of a
  substance is.
• 3) Complete Page 353 questions 1, 2, 3, 4, 7
• 4) Complete Page 343 questions 1, 2, 5, 6, 7
• 5) Complete Page 349 questions 5, 6
• 6) Complete Page 350 questions 7, 8ab, 9