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A vibration is one complete back and forth motion of an object.  Some vibrations are able to make sounds - like a guitar string vibrating back and forth.  The rate of vibration is measured in Hertz (Hz).

                           1 Hertz = 1 Vibration per Second

Sound cannot travel through space - it must go through a medium (a substance that allows sound waves to travel through it).

Sound travels in waves through the air (or other medium).  The air particles vibrate, creating compressions (where the particles are squished together) and expansions (where they pull aways from each other).  These compression waves are the sound waves.  For a good visual of this process, click here and look at the "Longitudinal Wave".

Wavelength is the distance from the top of one wave to the top of the next wave.

Frequency is the number of waves/vibrations that occur in one second.  This is related to wavelength, because shorter wavelengths give higher frequencies.  Frequency determines the pitch (the highness or lowness) of a sound.

Amplitude is the height of the wave.  This determines the volume (the loudness) of the sound.  The volume of sound is measured in decibels (dB).


Materials have natural frequencies that they vibrate at.  See the video of the Tacoma Narrows Bridge here.


Video of a sonic boom here.

The Ear
This list of ear parts goes with the study guide provided in class.  The diagram can also be found on page 392 of your textbook.
1. Pinna - Focuses sound into the ear canal.
2. Sound Waves
3. Ear Canal - Brings sound waves to the ear drum.
    You should never stick things into your ear canal (including
    fingers or Q-tips), as this can tear the eardrum.
4. Ear Drum - Vibrates when sound hits it.
5. Malleus (aka: Hammer) - Bone that carries vibrations to the
6. Incus (aka: Anvil) - Bone that carries vibrations to the stapes.
7. Stapes (aka: stirrup) - Bone that carries vibrations to the oval
    The malleus, incus, and stapes work together to carry
    vibrations to the inner ear.
8. Oval Window - Lets vibrations into the cochlea (inner ear).
9. Semicircular Canals - Help with balance and tell you your
    orientation in space.
10. Cochlea - Converts vibrations into nerve signals (impulses).
11. Auditory Nerve - Brings nerve signals to the brain from the ear.
12. Eustachian Tube - Equalizes the air pressure between the
      inside and the outside of the ear.
13. Ear Drum
14. Malleus (Hammer)
15. Incus (Anvil)
16. Stapes (Stirrup)
17. Oval Window
18. Watery Fluid - Carries vibrations through the cochlea.
19. Round Window - Lets vibrations out of the cochlea.
20. Cochlea
21. Hair Cells - Create nerve signals (impulses) from vibrations.
      Hair Cells are very delicate.  Very loud noises (such as having
      your headphones turned up too loud) can injure/kill them.
      Since nerve cells do not grow back, this can result in
      permanent hearing loss.

22. Auditory Nerve

Web Resources

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