5 2 Categories of Waves Mechanical Waves Require a medium (material) to travel throughExamples: water waves, sound wavesElectromagnetic Waves (covered in AP 2)Do not require a mediumExample: light travels through empty space
6 Wave Description Crest Trough Amplitude Wavelength Intensity of the wave.How much energy is transferred.WavelengthThe distance from one point on a wave to the same point on the next wave.
7 Wave Description Frequency Unit Equation 𝒇= # 𝒘𝒂𝒗𝒆𝒔 𝒕𝒊𝒎𝒆 How frequently a wave pulse occurs.UnitHertz (Hz)1 Hz = 1/seconds or s-1Equation𝒇= # 𝒘𝒂𝒗𝒆𝒔 𝒕𝒊𝒎𝒆
8 Wave Description Period Equation 𝑻= 𝒕𝒊𝒎𝒆 # 𝒘𝒂𝒗𝒆𝒔 The time (in seconds) that it takes for one wave to pass.EquationT = Period (in seconds)𝑻= 𝒕𝒊𝒎𝒆 # 𝒘𝒂𝒗𝒆𝒔
9 Wave Description 𝑻= 𝟏 𝒇 𝒇= 𝟏 𝑻 Frequency and Period are Inversely Related𝑻= 𝟏 𝒇𝒇= 𝟏 𝑻
10 Types of Waves Transverse Waves Matter moves perpendicular to the direction of wave movement.
11 Types of Waves Longitudinal Waves Matter moves parallel to the direction of wave movement.
13 Other Types of Waves!Raleigh WavesSeismic (earthquake) waves.
14 Wave MotionWaves transfer energy!Matter has no net movement.
15 Wave MotionWaves transfer energy!Matter has no net movement.
16 Wave Speed Equation Examples 𝒗=𝒇𝝀 A wave with a wavelength of 2 meters has a frequency of 50 Hertz. What is the velocity of the wave?Answer: 100 m/sv = wave velocity (in m/s) f = frequency (in Hertz) λ = wavelength (in meters)𝒗=𝒇𝝀
17 Wave SpeedExamplesOcean waves are washing up on shore with a velocity of 5 m/s. If they each have a length of 1.5 meters, what is the frequency of the ocean waves?Answer: 3.33 Hz
18 Wave InteractionsWhen two (or more) waves are travelling through the same medium they will interact with each other.The net displacement is the sum of the two waves.
19 Wave Interactions Example: Shown to the right are four different pairs of wave pulses that move toward and interact with each other. Rank, from most to least, the height of the peak that results when the two pulses coincide.Answer: A,B,D,C
20 ResonanceThe frequency of forced vibrations in an object matches its natural frequency, causing it to resonate.This creates a huge increase in amplitude.
21 Natural Frequency The special sound an object has when it vibrates. Every object has a specific frequency.
22 HarmonicsA harmonic is a whole number multiple of the natural frequency.
23 Standing WavesStanding waves in 1 dimension are formed when two identical waves travelling in opposite directions overlap.In practice, there is usually one wave which is reflecting back and forth between the two ends of a fixed length of medium. If the length is a suitable multiple of the wavelength, then the wave overlaps itself in a regular fashion and a standing wave is set up.
25 Standing WavesAt some points (nodes) destructive interference means that there is no net vibration of the medium, and at others (antinodes) the vibration is double the effect of a single wave.As a result, energy is not transferred by a standing wave, as it is with travelling waves, but is stored in the antinodes.
26 Boundary ConditionsAt a fixed end, a wave is reflected out of phase. Therefore, the on coming and reflected wave will always interfere destructively, producing a node.At a free end, a wave is reflected in phase. Therefore the oncoming and reflected waves will interfere constructively, producing an antinode.
27 Boundary ConditionsIn the case of stringed musical instruments, the strings are under tension and fixed at both ends.Wind instruments rely on a standing wave being set up in a column of air. The ends of the pipe may be open (free) or closed (fixed), although both ends cannot be closed!
28 Boundary ConditionsFor two close end boundaries, you end up with even number of quarter wavelengths.
29 Boundary ConditionsFor two open end boundaries, you also end up with even number of quarter wavelengths.
30 Boundary ConditionsFor one open end boundaries, you end up with odd number of quarter wavelengths.
31 Standing WavesAt some points (nodes) destructive interference means that there is no net vibration of the medium, and at others (antinodes) the vibration is double the effect of a single wave.As a result, energy is not transferred by a standing wave, as it is with travelling waves, but is stored in the antinodes.