2 What Are Waves? Wave – a disturbance that transfers energy -- the energy transferred through a wave can be carried from the disturbance, through the wave, to another objectEx: wind gives energy (a disturbance), creating waves on an ocean, and the ocean carries that energy to a boat, and the energy rocks the boat up and down-- the energy from the disturbance is transferred through a medium
3 Mediums Medium – the substance through which a wave travels -- in an ocean wave, water is the medium-- in sound waves, air is the mediumIt is important to understand that the wave DOES NOT CARRY the medium itself. It only moves energy through the medium.-- the ship doesn’t move on the waves, it only bobs up and down
4 What Causes Waves?Waves are created when a source of energy causes a vibration in a mediumVibration – a repeated back-and-forth or up-and-down motion-- some mediums can vibrate a lot with only a little energy input-- other mediums only vibrate a little with a lot of energy input-- the amount of vibration depends on the spacing and type of molecules within the medium
5 Types of WavesThere are three different types of waves, which are solely characterized by the way that they move.The three types of waves are:-- Transverse waves-- Longitudinal Waves-- Surface Waves
6 Transverse WavesTransverse waves – waves whose mediums move a right angles (perpindicular) to the direction of overall wave travel-- if the wave below moves left-to-right, the medium will move up-and-down-- like whipping a ropeParts of a Transverse WaveCrest – the “high” parts of the transverse waveTrough – the “low” parts of the transverse wave
7 Longitudinal WavesLongitudinal Waves – waves whose mediums move in the same direction as overall wave travel-- like squeezing and releasing a slinky spring-- longitudinal waves are often called compressional wavesParts of a Longitudinal waveCompressions – areas where the molecules in the medium are tightly squeezed togetherRarefactions – areas where the molecules in the medium are spread apart
8 Surface WavesSurface Waves – waves that form at the boundary between two different mediums-- the bouncing of waves vibrating differently create circular-shaped waves
9 Wave PropertiesDespite the different types of waves, all waves share the same basic properties:-- amplitude-- wavelength-- frequency-- speedWhen figuring out these properties on either longitudinal or transverse waves, it is necessary to remember the following:Crests on a transverse wave are equal to compressions on a longitudinal waveTroughs on a transverse wave are equal to rarefactions on a longitudinal wave
10 AmplitudeAmplitude – the maximum distance the particles of a medium move from their rest positionFor a transverse wave:-- to find amplitude, you measure the height of the crest from the REST POSITION (or the depth of the trough)For a longitudinal wave:-- to find amplitude, you measure how strongly compressed the compressions are (or how far apart the rarefactions are spread)amplitude
11 WavelengthWavelength – how much of the medium is between corresponding parts of a repeating wave-- wavelength is measured in meters, and is represented in formulas by the Greek letter lambda (λ)For a transverse wave: you find wavelength by measuring the distance between crests (or troughs)For a longitudinal wave:-- you find wavelength by measuring the distance between compressions (or rarefactions)wavelength
12 FrequencyFrequency – the number of complete waves that pass a specific point in a given amount of time (usually 1 second)-- frequency is measured in a unit called Hertz (Hz), which is equal to waves/second (really is the unit per second)-- frequency is represented by the Greek letter nu (ν)To find the frequency of any wave, either count the number of crests or the number of compressions that pass a specific point in a given amount of time, then solvePeriod – the amount of time it takes for one complete wave to pass-- period is the inverse of frequencyEx: If a wave has a frequency of 3 Hz (3 waves pass per second, then its period is 1/3 second (it takes 1/3 of a second for one wave to pass)
13 Speed = wavelength x frequency The speed of a wave is how much of a medium passes by a specific point in a given amount of time-- speed is in the units of meters per second (m/s)The speed of the wave is entirely determined by the medium through which the wave passes.We can calculated wave speed with the following equation:Speed = wavelength x frequencyORs = λ x νOf course: λ = (s / ν) and ν = (s / λ)
14 Practice Problems An ocean wave passes a buoy 5 times in 20 seconds. a) What is the frequency of this wave?b) What is the period of this wave?c) If the wave has a wavelength of 10 meters, what is the speed of this wave?
15 More Practice Problems The speed of a rope is 40 m/s and its wavelength is 5 m.a) What is the frequency of this wave?b) What is the period of this wave?3. A wave with a period of 0.2 seconds travels at a speed of 60 m/s. What is the wavelength of this wave?