P199: Introduction & Start of Sound
description
Transcript of P199: Introduction & Start of Sound
![Page 1: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/1.jpg)
P199: Introduction & Start of SoundLecturer Stacy McCormackPhysics Department, Indiana University
![Page 2: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/2.jpg)
Topic 1: SoundVIBRATIO
N
![Page 3: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/3.jpg)
Sound in space?
MISCONCEPTION!Molecules in solid, liquid, gas
![Page 4: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/4.jpg)
Sound Waves & TermsLongitudinal 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)
![Page 5: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/5.jpg)
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
![Page 6: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/6.jpg)
Frequency vs. Wavelength
![Page 7: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/7.jpg)
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
NOTE: Distance between adjacent node and antinode is ¼ wavelength
![Page 8: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/8.jpg)
Tuning fork
Antinode: MAXIMUM VIBRATION
Node: NO VIBRATION
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
![Page 9: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/9.jpg)
Pitch and Tuning ForksLarge distance between node and antinode
Large wavelength
Small frequency
Low pitch
Small distance between
node and antinode
Small wavelength
Large frequency
High pitchRemember: distance between node and antinode is ¼
wavelengthSo to find wavelength, take N-A distance and multiply by
4!
N N
A A
![Page 10: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/10.jpg)
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?
A AN
![Page 11: P199: Introduction & Start of Sound](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163c2550346895dd4e84e/html5/thumbnails/11.jpg)
Demonstration with two twists
Closing off one end makes a node
Makes wavelength longer than if just left open
Lowers pitch
N A
Using scissors, add a hole at the halfway point
Creates an antinode
Shortens wavelength
Higher pitchN NA AA