13Frequency, amplitude, and wavelength You can think of a wave as a moving series of high points and low points.A crest is the high point of the wave.A trough is the low point.
14FrequencyThe frequency of a wave is the rate at which every point on the wave moves up and down.Frequency means “how often”.
15AmplitudeThe amplitude of a water wave is the maximum height the wave rises above the level surface.
16WavelengthWavelength is the distance from any point on a wave to the same point on the next cycle of the wave.The distance between one crest and the next crest is a wavelength.We use l (lambda) to represent wavelength.
17The speed of wavesThe speed of a water wave is how fast the wave spreads, NOT how fast the water surface moves up and down or how fast the dropped ball moves in the water.How do we measure the wave speed?
18The speed of waves A wave moves one wavelength in each cycle. Since a cycle takes one period, the speed of the wave is the wavelength divided by the period.
19The speed of waves The speed is distance traveled divided by time. Distance is equal to wavelength.Time is equal to the period.Speed = Distance = WavelengthTime PeriodSince Period is 1/frequency, we can replace them.Speed = Wavelength x Frequencyv = · f
20Solving ProblemsThe wavelength of a wave on a string is 1 meter and its speed is 5 m/s.Calculate the frequency and the period of the wave.
21Solving Problems Looking for: Given Relationships: Solution …frequency in hertz…period in secondsGiven… = 1 m; s = 5 m/sRelationships:s = f x or f = s ÷ f = 1/T or T = 1/fSolutionf = 5 m/s ÷1 m = 5 cycles/sT = 1/5 cycles/s = .2 sf = 5 HzT = 0.2 s
22Solving ProblemsThe musical note A above middle C has a frequency of 440 Hz. If the speed of sound is known to be 331 m/s, what is the wave length of this note?You are given:f = 440 Hzv = 331 m/s1. Write the Equationv = f x λ2. Rearrange for valueλ = v/f3. Plug in known values to solveλ = (331 m/s)/(440 Hz)λ = 0.80 meters
23Four wave interactions When a wave encounters a surface, four interactions can occur:reflection,refraction,diffraction, orabsorption.
25Wave interactionsA boundary is an edge or surface where things change.Reflection, refraction, and diffraction usually occur at boundaries.
26Wave interactionsDiffraction usually changes the direction and shape of the wave.When a plane wave passes through a small hole diffraction turns it into a circular wave.
27ResonanceEverything has a natural frequency that it can make it oscillate.Examples:Jump RopeWhen it is moved correctly, it can be used for jumping.When it is moved incorrectly, it fluctuates, but cannot be used for jumping.SwingPushes are synchronized so that a push is applied when the swing is up, and the swing begins to move higher.
28Standing wavesA wave that is confined in a space is called a standing wave.A string with a standing wave is a kind of oscillator.
2924.2 Standing wavesThe place on a harmonic with the greatest amplitude is the antinode.The place where the string does not move (least amplitude) is called a node.
3024.2 Standing wavesIt is easy to measure the wavelength of a standing wave on a string.
31Wave InterferenceWhen two or more waves come in contact with each other, they interfere with each other.Constructive interference happens when waves add up to make a larger amplitude.Occurs when the waves are “in phase.”Destructive interference happens when waves add up to make a smaller amplitude.Occurs when the waves are “out of phase.”