Resonance,%20Sound%20Waves%20and%20The%20Ear

1
Resonance, Sound Waves and The Ear
2
What does the natural frequency depend upon?

• The natural frequency depends on many factors,
  such as the tightness, length, or weight of a
  string.
• We can change the natural frequency of a system
  by changing any of the factors that affect the
  size, inertia, or forces in the system.
• For example, tuning a guitar changes the natural
  frequency of a string by changing its tension.

3
Resonance

• You can think of resonance as having the natural
  frequency of the system exactly in tune with your
  force. Each cycle of your force exactly matches
  each cycle of the system.
• As a result, each push adds to the next one and
  the amplitude of the oscillation grows.
• Two tuning forks with the same natural
  frequencyone vibrating nearby will cause the
  other to vibratethe forks are connected by air
  molecules.

4
Natural Frequency--Forced Vibration--Resonance

• Natural frequency the frequency (or frequencies)
  at which an object naturally vibrates when
  disturbed.
• Forced Vibration a vibrating object in contact
  with another object causes it to vibrate at the
  same frequency.
• Resonance Condition occurring when the
  frequency of a vibration of one object matches
  the natural frequency on another object and
  causes it to dramatically increase in amplitude
• Resonance can occur whenever successive impulses
  are applied to a vibrating object in rhythm with
  its natural frequency. (pushing someone on a
  swing)
• http//www.youtube.com/watch?vWDZmjzxaxhs

5
26.6 Natural Frequency vs. Forced Vibration

• When any object composed of an elastic material
  is disturbed, it vibrates at its own special set
  of frequencies, which together form its special
  sound.

We speak of an objects natural frequency, the
frequency at which an object vibrates when it is
disturbed.
A forced vibration occurs when an object is made
to vibrate by another vibrating object that is
nearby.
A natural frequency is one at which minimum
energy is required to produce forced vibrations
and the least amount of energy is required to
continue this vibration.
6
26.8 Resonance

• An object resonates when there is a force to pull
  it back to its starting position and enough
  energy to keep it vibrating.
• It is the frequency or frequencies at which an
  object will most easily vibrate.

7
Examples of Resonance

• Sympathetic vibrations
• speakers buzzing
• cilia in cochlea of inner ear vibrating
• Building up amplitude
• girl pushed on swing gains height
• one tuning fork causes another to vibrate without
  direct physical contact
• Tacoma Narrows Bridge Collapse

8
26.8 Resonance
If the frequency of a forced vibration matches an
objects natural frequency, resonance
dramatically increases the amplitude. You pump a
swing in rhythm with the swings natural
frequency. Timing is more important than the
force with which you pump. Even small pumps or
pushes in rhythm with the natural frequency of
the swinging motion produce large amplitudes.
9
26.8 Resonance

1. The first compression gives the fork a tiny push.

10
26.8 Resonance

1. The first compression gives the fork a tiny push.
   
2. The fork bends.

11
26.8 Resonance

1. The first compression gives the fork a tiny push.
   
2. The fork bends.
3. The fork returns to its initial position.

12
26.8 Resonance

1. The first compression gives the fork a tiny push.
   
2. The fork bends.
3. The fork returns to its initial position.
4. It keeps moving and overshoots in the opposite
   direction.

13
26.8 Resonance

1. The first compression gives the fork a tiny push.
   
2. The fork bends.
3. The fork returns to its initial position.
4. It keeps moving and overshoots in the opposite
   direction.
5. When it returns to its initial position, the next
   compression arrives to repeat the cycle.

14
Tacoma Narrows Bridge

• http//www.youtube.com/watch?v3mclp9QmCGs

now
Then (July 1940)
15
(No Transcript)
16
Sound waves and the Ear
What is the audible range of frequencies for a
human? 20 -20,000 Hz
Relative intensity of sound wave is volume and is
measured in decibels (dB)
What type of wave is a sound wave? Mechanical and
Longitudinal
The frequency of a sound wave is called pitch.
Like all mechanical waves, sound waves can only
travel through matter
17
BASIC FUNCTION OF THE EAR

• The ear converts changes in air pressure due to
  sound waves to nerve impulses that signal the
  brain

Eardrum vibrates at same frequency as tuning fork
and with a certain intensity
compression
256 Hz
256 Hz
rarefaction
18
The Ear
Semicircular canals (for balance)
3 tiny bones (hammer, anvil and stirrup)
cochlea
Pinna
19
Cochlea of the Human Earcilia and nerves in
different regions in the cochlea resonate to
specific frequencies of sound waves. The region
that resonates at 256 Hz lights up and signals
your brain via the nerves.
256 Hz
20
Hearing Problems

• conductive hearing loss (interferes with the
  transfer of sound vibrations)
• sensory hearing loss (affects the cochleas
  ability to resonate from 20 - 20,000 Hz.)
• neural hearing loss (affects the connection
  between the cochlea and the brain.)

21
Hearing Corrections

• Repairs to the conductive parts of the ear
• Cochlear implants (addresses frequency
  deficiencies)
• Hearing aids (increase amplification)

22
Main Parts of the Ear

• Inner Ear
• Middle Ear
• Outer Ear

outer
inner
middle
23
Outer Ear

• Structures the pinna, ear canal and eardrum.
• Purpose to receive, focus (or amplify) and
  transmit sound vibrations to the middle ear.

Eardrum vibrates at same frequency as tuning fork
256 Hz
256 Hz
24
Middle Ear

• Structure Ear bones (hammer, anvil and stirrup
  are the three tiniest bones in the human body)
• Purpose To transmit sound
• vibrations from the eardrum
• to the inner ear.

25
Inner Ear

• Structure Cochlea
• Purpose The fluid in the cochlea receives sound
  vibrations from the stirrup, causing tiny hairs
  inside the cochlea to vibrate, which stimulates
  auditory nerves connected
• to the brain.

256 Hz