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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

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P199 introduction start of sound

P199: Introduction & Start of Sound

Lecturer Stacy McCormack

Physics Department, Indiana University


Topic 1 sound

VIBRATION

Topic 1: Sound


Sound in space

MISCONCEPTION!

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


P199 introduction start of sound

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


Frequency vs wavelength

Frequency vs. Wavelength


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

Antinode: MAXIMUM VIBRATION

Node: NO VIBRATION


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

A

A

N

N

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

A

A

N

  • 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

N

A

Closing off one end makes a node

Makes wavelength longer than if just left open

Lowers pitch

N

A

N

A

A

Demonstration with two twists


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