Waves & acoustics

Wiki page for waves

Water wave

Pressure wave in a solid
Shear wave in a solid
Spring wave

Waves on a string

Time warp video of a guitar
PHET simulation for waves on a string

Electromagnetic wave

Crowd wave

Wave_speed = wavelength * frequency

The speed of sound in air is ~ 330 meters per second. In the left photo, the plane is moving slower than the sound waves, and in the right panel it's moving faster.

Wave refraction
The wave travels through a fast medium on the left and then encounters the slow medium on the right. The wave frequency is the same in both cases, and so when the wavespeed decreases, the wavelength gets shorter. A wave bends (refracts) if the wave speed changes.
Musical scales

Online piano Online piano Tone generator Equal temperament
Just temperament
Physics of music
Note Interval Equal Just Ratio Major Minor tuning tuning scale scale A Unison 1.000 1.000 1/1 * * A# or Bflat Minor second 1.059 B Major second 1.122 8/9 * * C Minor third 1.189 1.200 6/5 * C# Major third 1.260 1.250 5/4 * D Fourth 1.335 1.333 4/3 * * D# or Eflat Tritone 1.414 E Fifth 1.498 1.500 3/2 * * F Augmented fifth 1.587 * F# Sixth 1.682 1.667 5/3 * G Minor seventh 1.782 * G# or Aflat Major seventh 1.888 * A' Octave 2.000 2.000 2/1 * * A = 2^( 0/12) = 1 A# = 2^( 1/12) = 1.059 B = 2^( 2/12) = 1.122 E = 2^( 7/12) = 1.498 A' = 2^(12/12) = 2 Instruments that use equal tuning: pianos, wind instruments, trumpets. Instruments that use just tuning: singers, stringed instruments, trombones. Percussion instruments don't produce pure tones. Auto-tune

Dissonance: If two sound waves have frequencies that are related by a small integer ratio, they sound consonant together. Otherwise they sound dissonant. Wiki page for consonance and dissonance If the frequencies close to an integer ratio but not exact, beat frequencies are generated. Wiki page for beat frequencies

"In Vain" by the Argento Ensemble

Auditory sensitivity

Frequency (Hertz) < 20 Infrasound. Elephant hearing 20 - 100 Bass & subwoofers 100 - 1000 Midrange of human hearing 1000 - 2000 Soprano >20000 Dolphin and bat sonar Humans hear frequencies from 20 Hertz to 20000 Hertz. Wiki page for elephants and infrasound
Video of elephants and infrasound
Dolphins and ultrasound

Wave interference

Left: waves adding constructively. Right: waves adding destructively. Wiki page for noise cancelling headphones
PHET simulation for wave interference
PHET simulation for waves on a string

Resonance Wiki page for resonance
Tacoma Narrows bridge collapse
Time Warp: Breaking a wine glass