Ch 14 Vibrations and Waves Periodic Motion Periodic
Ch. 14 - Vibrations and Waves
Periodic Motion • Periodic motion - any type of motion that repeats or has a cyclic pattern • Examples: pendulum, spring, circular motion • Assume that all periodic motion is simple harmonic motion: the force added is directly proportional to the distance moved
• Pendulum - An object suspended by a string or rope that swings back and forth • Maximum velocity occurs at the bottom of the swing (KE) • Minimum velocity occurs at the top of the swing (PE) • We define the period as the time it takes the object to travel from one side to the other and back T : period (s) L : length of string (m)
Swinging Lab Objective Find the acceleration of gravity Materials Pendulum, stopwatch, meter stick, calculator Procedures Record L for your pendulum. Measure the period. Solve for g. How close to the actual value are you? If less than 10%, stop; otherwise, try again.
Spring - metal or plastic shaped in a spiral pattern, designed to store/release energy • When compressed or stretched, elastic potential energy is stored • Amount of force required to store energy is based on the spring constant • Assume all springs obey Hooke’s Law (force exerted is equal to the spring constant times the distance the spring is compressed or stretched from its equilibrium position). F : restoring force (N) k : spring constant (N/m) PE : stored energy in spring (J) x : distance stretched or compressed (m)
WAVE CHARACTERISTICS • Waves: repeating disturbances that transfer energy through matter or space • Crest: highest point of wave • Trough: lowest point of wave • Amplitude: distance from rest position to crest or trough
• Wavelength (measured in meters) • Distance between two similar points on a wave • Frequency (measured in Hertz) • Number of wavelengths that pass a fixed point each second • Wave speed (measured in meters per second) • How fast a wave is traveling
v=lƒ v : wave speed (m/s) l : wavelength (m) ƒ : frequency (Hz)
frequency (ƒ) • Number of complete oscillations a wave makes each second. ƒ = 1/T (the frequency of a wave is equal to the reciprocal of the period).
2 TYPES OF WAVES TRANSVERSE motion and oscillation are perpendicular ex. Light, radio waves LONGITUDINAL (COMPRESSIONAL) motion and oscillation are parallel ex. Sound
PRINCIPLE OF SUPERPOSITION • Waves can algebraically interact with each other • This interaction is called interference • Destructive: waves subtract from each other • Constructive: waves add to each other
Ch 14 HW: p 397 - 400 70. 71. 74. 77. 81. 84. 88. - 0. 12 m 0. 35 J 0. 21 m 0. 29 m/s; 0. 21 s 1350 m See picture 2. 4 s a. b. c.
Ch. 15 - Sound (and Music)
• Intensity (measured in decibels) • Amount of energy transmitted by a wave • Loudness • Human perception of sound intensity • Pitch (measured in Hertz) • The relative high or low frequency of a sound wave
Longitudinal wave (sound) • Must have a medium (material) to travel through • Points of highest pressure are the crests • Points of lowest pressure are the troughs • Distance between crests or troughs is the wavelength
How we hear: • Outer ear – gathers sound waves • Middle ear – amplifies waves • Inner ear – converts waves to nerve impulses
Doppler Effect • The change in frequency of a wave due to the motion of the source or receiver • If the wave is moving closer to the receiver, the frequency (pitch) increases • If the wave is moving away from the receiver, the frequency (pitch) decreases
Doppler Effect Equation nd = ns (v ± vd) / (v vs) where nd is the detector frequency (Hz) ns is the source frequency (Hz) v is the speed of sound (m/s) vd is the speed of the detector (m/s) vs is the speed of the source (m/s) ±
52. 53. 55. 58. 69. 70. 1715 m 510 m 9. 8 x 104 Hz 1. 45 x 103 m/s 350 Hz 335 Hz; 356 Hz 280 Hz; 263 Hz
- Slides: 20