P199: Introduction & Start of Sound

1. P199: Introduction & Start of Sound Lecturer Stacy McCormack Physics Department, Indiana University

2. VIBRATION Topic 1: Sound

3. MISCONCEPTION! Molecules in solid, liquid, gas Sound in space?

4. 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

5. 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

6. Frequency vs. Wavelength

7. 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

8. 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

9. 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!

10. 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

11. 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