Waves and Sound

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Sound Wave is a mechanical wave generated by vibrating objects in an elastic medium.
- Medium: Air, solids, and liquids can transmit sound waves.
Misconception: Radio waves are electromagnetic waves, not sound waves.

Speed of Sound varies with the medium.
- Air: Speed increases with temperature.
- Equation: Vsound = 331.5 m/s + (0.6 x Temp)
- Speed: Air = 343.5 m/s, Water = 1482 m/s, Steel = 5960 m/s

Temperature and Sound Speed: Sound moves faster in warmer air.
- Equation Example: Vs = 331.5 m/s + (0.60 T)
- Calculations: Room temperature (20.0ºC) = 343.5 m/s

Frequency and Source: Frequency and period of a sound wave depend on the source's properties.
- Natural Frequency: Each source has a unique natural frequency.

Wavelength: Depends on wave speed and period.
- Equations: Vsound = f x λ or Vsound = λ T

Wavelength and Frequency: Inversely related when speed is constant.
- Relation: Low Frequency = High Wavelength, High Frequency = Low Wavelength

Wave Interference: Occurs when two waves meet.
- Constructive Interference: Adds up amplitudes.
- Sound Example: Louder sound produced.

Destructive Interference: Waves cancel out.
- Sound Example: Softer sound produced.

Beats: Interference of sound waves with slightly different frequencies.
- Result: Creates louder or softer sounds.
- Formula: fbeat = f1 – f2

Echoes: Sound wave reflection off a boundary.
- Factors: Speed of sound, distance, and time.
- Equations: distance = Vsound x 2, time = 2

Solving Echo Problems: Finding distance and time.
- Scenarios: Given time or distance to find the other.

Echo Problems Examples: Calculations involving speed of sound.
- Scenarios: Man yelling towards a building, dolphin sending sound waves.

Sound Waves in Air: Velocity determined by air properties.
- Standard Speed: 343.5 m/s
- Frequency Determination: Vsound = λ f

Sound Waves in Air: Using standard speed for calculations.
- Calculations: Wavelength, distance, frequency of sound waves.

Resonance involves two sets of frequencies in the source
- Object vibrates at its natural frequency when disturbed
- Natural frequency depends on object's physical properties
Forced vibration occurs when object vibrating at natural frequency is disturbed
- Two disturbances combine similar to interference
- Vibrations add together if in the same direction, cancel out if in opposite directions
Resonance occurs when forced vibrations match natural vibrations
- Vibrations add together to create larger amplitude
- Amplitude continues to increase until system breaks under strain

Tacoma Narrows Bridge collapsed due to resonance from vortex shedding caused by wind
- Wind forced the bridge to sway at its natural frequency
- Amplitude of swaying increased until the bridge tore apart

Sound waves are longitudinal waves created by air molecules forming high and low-pressure areas
Intensity is a measure of the power of a wave in a specific area
- Threshold of Hearing is the lowest intensity audible
- Threshold of Pain is the highest intensity without causing ear damage
Decibel is the unit of sound, a difference in intensity that is "just noticeable"
Loudness is a combination of frequency and intensity perceived by humans
- Humans perceive different frequencies differently
- Example: 4000 Hz sound wave perceived louder than 100 Hz at the same intensity