4 Mechanical Waves Not all waves travel through a medium. Mechanical waves only transfer energy through matter.There are two types:TransverseLongitudinal (or compressional)Wave motion transfers energy without transferring matterClick here for a visual of mechanical waves (at bottom of page)
5 Transverse Waves: matter in the medium moves perpendicular to direction the wave travels
6 Longitudinal (Compressional) Waves: matter in the medium moves parallel to the direction the wave travels
7 Combination Waves: Ocean Water An ocean wave is a combination of transverse and longitudinal waves.The individual particles move in ellipses as the wave disturbance moves toward the shore.
8 Concept Check What is a wave? What are the two types of mechanical waves?
9 Wave Properties There are four wave properties: Amplitude Wavelength FrequencyWave Velocity
10 Amplitude is a measure of the amount of energy in a wave In Transverse Waves…In Compressional Waves… look at how dense the compressions are. The more dense, the higher the amplitude
11 Frequency is the number of wavelengths that pass a fixed point each second f = waves/secondSI unit = Hertz (Hz)As Frequency ,WavelengthIs this a high- or low-frequency wave?
12 Wavelength is the distance between a point on one wave and the identical point on the next wave
13 Calculating Frequency F = 1/TRemember T…Called “period”The time it takes for one wave to pass a given pointMeasured in secondsWhat is the frequency of ocean waves that wash up on the shore every 2.5 seconds?
14 Velocity = wavelength x frequency Wave Velocity is how “fast” the wave movesVelocity = wavelength x frequencyv = λfv = velocity (m/s)λ = wavelength (m)f = frequency (Hz)
15 ExampleA sound wave travels from a speaker to your ear. If it has a frequency of 12,000 Hz and a wavelength of 2 cm, what is its velocity?
16 List and describe the four Concept CheckList and describe the fourwave properties.
17 How do waves differ from one another? 1) Energy, 2) Velocity, 3) AppearanceTRANSVERSEVS.COMPRESSIONAL
18 Some other terms to know… PeriodTime for one wave to pass a given point (seconds)Inverse of frequencyNodeThe point where the medium is never displacedOn the “normal” lineAntinode –The point of maximum displacementOccurs at the wave’s crest
20 Wave Behavior All waves of all types exhibit these four behaviors: ReflectionRefractionDiffractionInterference
21 The “bouncing back” of a wave ReflectionThe “bouncing back” of a wave
22 The Law of Reflection says… Angle of Incidence = Angle of Reflection
23 RefractionThe change in wave direction at the boundary between two different mediaDifferent materials allow waves to travel at different speedsAngle of RefractionAmount of bendingDepends on how much the material changes the wave’s speed
24 Diffraction The bending of a wave around a barrier or a small opening It’s the same process for sound AND light
25 InterferenceWhen two or more waves (blue and red) exist in the same medium, each wave moves as though the other were absentWhen they meet, they interfere with one another and make a new wave (green).Visualization of Interference
26 Constructive or Destructive? Constructive Interference – 2 waves combine to form a new wave with a larger amplitude.Destructive Interference – 2 waves combine to produce a wave with a smaller amplitude.
27 Wave Formulas f = 1/T v = λ f f = frequency (Hz) T = period (s) v = velocity (m/s)λ = wavelength (m)f = frequency (Hz)