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P199: Introduction & Start of Sound. Lecturer Stacy McCormack Physics Department, Indiana University. VIBRATION. Topic 1: Sound. MISCONCEPTION!. Molecules in solid, liquid, gas. Sound in space?.

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p199 introduction start of sound

P199: Introduction & Start of Sound

Lecturer Stacy McCormack

Physics Department, Indiana University

sound in space


Molecules in solid, liquid, gas

Sound in space?
sound waves terms

Longitudinal wave-individual vibrating objects move right or left and the disturbance also moves right or left (ex. sound wave)

Transverse wave-individual objects move up and down, but disturbance moves right or left (ex. water wave)

Amplitude-height from rest position (determined by the amount of energy), loudness

Wavelength-distance between two like molecules (humans hear from 0.65 in to 54 ft, musical note A is 31 in)

Sound Waves & Terms

Frequency & Pitch

  • Frequency-how quickly the vibration is occurring, how much time is needed to complete a cycle
  • High frequency-very fast, many cycles per second
  • Low frequency-slower, less cycles per second
  • Measured in Hertz (Hz)-known as cycles/second
  • Musical note A has a frequency of 440 Hz
  • Humans can hear 20 Hz-20,000 Hz
  • Pitch is our perception of frequency
  • High pitch=high frequency=soprano singer
  • Low or deep pitch=low frequency=bass singer
why are some sounds high pitched and others low pitched

Node-a place where there is NO VIBRATION-the molecule always remains in the same location

Antinode-a place where there is MAXIMUM VIBRATION-the molecule is moving

Why are some sounds high-pitched and others low-pitched?

NOTE: Distance between adjacent node and antinode is ¼ wavelength

tuning fork

Large or long distance between node and antinode=

large wavelength=

small frequency=low pitch

Small or short distance between node and antinode=

small wavelength=

large frequency=high pitch

Tuning fork



pitch and tuning forks

Large distance between node and antinode

Large wavelength

Small frequency

Low pitch

Small distance between node and antinode

Small wavelength

Large frequency

High pitch





Pitch and Tuning Forks

Remember: distance between node and antinode is ¼ wavelength

So to find wavelength, take N-A distance and multiply by 4!

drinking straw demonstration




  • Two antinodes at the ends because molecules have maximum vibration
  • Since antinodes are always separated by nodes, there must be a node in the center
  • Can determine wavelength
  • Longer straw=higher or lower pitch?
Drinking straw demonstration
demonstration with two twists

Using scissors, add a hole at the halfway point

Creates an antinode

Shortens wavelength

Higher pitch



Closing off one end makes a node

Makes wavelength longer than if just left open

Lowers pitch






Demonstration with two twists