2 Waves and Oscillations Pendulum swinging back and forth shows how oscillations can create waves.
3 WAVES Energy transfer: by doing work, by heat, or by waves! Wave: a disturbance (vibration) that travelsmechanical waves require a material medium (solid, liquid, or gas) – particles vibrate in simple harmonic motion (water, sound, earthquake waves)2 types – transverse and longitudinalelectromagnetic waves travel through a material or a vacuum – vibrating electric and magnetic fields (radio, microwave, infrared, visible light, ultraviolet, x-ray, gamma rays)
4 WAVESTransverse waves: vibrations are perpendicular to wave direction
5 WAVES Longitudinal waves: vibrations parallel to wave direction rarefaction
6 WAVESFrequency, f: number of waves each second, unit: Hertz (Hz) Hz = 1 wave/secPeriod, T: time for one wave to pass, unit: s f=1/TWavelength, l: distance between identical points on two waves, unit: m
7 WAVES Amplitude, A: maximum displacement from equilibrium, unit: m Wave speed, v: speed of the wave, not the particles, unit: m/s v=fluse difference in wave speeds to find distanceex: lightning & thunder
8 WAVE INTERACTIONSReflection: waves "bounce back" at boundary
9 WAVE INTERACTIONSLaw of Reflection: qi = qr i: incidence, r: reflection
10 WAVE INTERACTIONSRefraction: wave path bends as wave crosses boundary. Note that speed & wavelength change as wave moves into new medium, but frequency remains constant.
11 Refraction Examples1. Dish filled with water Light through glass
12 Refraction RulesWhen a wave goes from fast to slow mediums the wave will bend toward the normal.When a wave goes from slow to fast mediums the wave will bend away from the normal.Vi Sin qr = Vr Sin qi
13 WAVE INTERACTIONSDiffraction wave spreads out or “bends” beyond edge of barrier
14 WAVE INTERACTIONSDiffraction greatest when l is greater than or equal to the size of opening or object
15 SOUND INTERACTIONS Resonance (sympathetic vibration) objects have natural vibrating frequencysending waves to an object at at its natural frequency will make it vibratepushing a child on a swingusing microwaves to heat up water
31 SOUND INTERACTIONSThe Doppler Effect: apparent change in frequency due to motion of source or listener
32 SOUND INTERACTIONSWave speed stays constant, remember wave speed depends on medium.Frequency changes and wavelength changesWhen source or observer moves toward each other wavelength decreases and frequency increases.When source or observer moves away from each other wavelength increases and frequency decreases
33 SOUND INTERACTIONSRadar: uses Doppler Effect in radio waves reflected off an object to determine its speed (speed traps, locating enemy aircraft)Red shift (decreased frequency) and Blue shift (increased frequency) of light tells astronomers whether a star or galaxy is moving toward or away from Earth.
35 SOUND INTERACTIONS The Doppler Effect sound barrier: “pile-up” of sound waves (pressure) in front of object traveling Mach 1sonic boom: cone-shaped pressure pulse following an object traveling at supersonic speeds (bow wave, also called water wake, following a speedboat)
38 QUIZ 5.4The speed of sound in earth is 3500 m/s. An earthquake wave, frequency 5 Hz, travels from its source to a distant mountain range and returns in 3.4 minutes.(a) How far away is the mountain range?(b) What is the wavelength of the earthquake wave?(c) If the mountain range was moving away at 0.50 m/s. what would be the frequency of the reflected wave?357,000 m700 m5.00 Hz
39 UNIT 5 REVIEW f = 1/T v = fl qi = qr visinqr = vrsinqi node dist = l/2 loop height = 4Av = TI = P/4pr2b = 10log(I/I0)I0 = 1×10-12 W/m2open pipe l = 2Lclosed pipe l = 4Lx = vt