2 What is a wave?A wave is a repeating disturbance or movement that transfers energy through matter or spaceWaves transfer energy NOT matterMedium: the matter through which a wave travels; i.e. water, air
5 Mechanical Waves Waves that can travel only through matter There are two types:Transverse waves (water, and some seismic waves)Longitudinal waves (sound, spring)Requires a medium!!!!!!!
6 Longitudinal (compressional) Waves Particles in the medium move parallel to the direction of the waves. particle motion wave motion The dense areas are called compressions.The less dense areas are rarefactions.
7 Transverse WavesParticles in the medium move perpendicular to the direction of the waves.wave motionparticlemotion
8 Parts of a Wave Crest: the highest point (top) of a transverse wave. Trough: the lowest point (bottom) of a transverse wave.Wavelength: the distance from any point on a wave to the same point on the next wave. (ex: crest to crest)Amplitude: the height measured from the resting position.
10 Seismic WavesSeismic waves are a combination of compressional and transverse waves1. They can travel along the earth’s surface2. When objects on the Earth’s surface absorb some of the energy carried by seismic waves, they move and shakeCompressionalTransverse
11 Greater amplitude = more energy. Measures the amount ofenergy in a wave.Greater amplitude = more energy.
12 FREQUENCYThe rate at which waves pass (the # of full wavelengths that pass a point in one second).Symbol: fUnit: Hertz (Hz)1 Hertz = 1 vibration per secondFrequency is 1 / T
13 WAVE SPEED How fast a wave moves. Symbol: v Unit: m/s Wave speed is determined by the medium. Generally, waves pass through solids faster b/c particles are closer and can pass vibrations to each other more quickly.
14 EQUATIONS v = f · λ f = v / λ λ = v / f v UNITS: λ = meters (m) Wave speed = frequency times wavelengthv = f · λ f = v / λλ = v / fUNITS: λ = meters (m)f = Hertz (Hz)v = m/svf λ
15 The string of a piano that produces the note middle C vibrates with a frequency of 264 Hz. If the sound waves produces have a wavelength of 1.30 m in air, what is the speed of sound in air?f = 264 Hzλ = 1.30 mv = ?v = 264 Hz (1.30 m)v = f · λv = m/s
16 A water wave has a speed of 1. 3 m/s A water wave has a speed of 1.3 m/s. A person sitting on a pier observes that it takes 1.2 s for a full wavelength to pass the edge of the pier. What is the wavelength of the water wave?v = 1.3 m/sT = 1.2 sf = 1 / T = 1 / 1.2 s= 0.83 Hzλ = ?λ = 1.3 m/s / 0.83 Hzλ = v / fλ = 1.57 m