10Parts of a Transverse Wave Crest- the highest part of the waveTrough- the lowest part of the wave
11Another type of mechanical wave… Longitudinal WaveLet me demonstrate…These waves move the medium parallel to the direction in which the waves travel.In this example, the coils in the Slinky move back and forth parallel to the motion of the wave.
12Parts of a Longitudinal Wave Compression- parts where the particles of the medium are close togetherRarefaction- parts where the particles of the medium are spread out, or rarifiedSound is a longitudinal wave. In air, sound waves cause air particles to move back and forth.
14Think back to yesterday when you formed a transverse wave with the class… Remember when we “sent the wave back” across the row?This is called reflection.Reflection is when a wave or object hits a surface through which it cannot pass and therefore it bounces back.
15What are some types of reflection that you can think of? Echo (reflection of sound)Mirror (reflection of light)Ball bouncing (reflection of an object)
16Refraction (NOT Rarefaction or Reflection!) When a wave enters a new medium at an angle, one side of the wave changes speed before the other side, causing the wave to bend, or refract.The bending of waves due to a change in speed is called refraction. This only happens when the wave enters the new medium at an angle.
17What are some examples of refraction that you can think of?
18Another type of wave bending… When a wave moves around a barrier or through an opening in a barrier, it bends and spreads out—this is called diffraction.Let’s look at a few examples of diffraction…
21Two waves can overlap when they meet. Interference is the interaction between waves as they meet.There are two types of interference:ConstructiveDestructive
22Constructive Interference A picture (or a video) is worth a thousand words...Constructive interference is when waves combine to make a larger wave.
23Destructive Interference This is when 2 waves combine to make a smaller wave.Destructive interference occurs when the crest of one wave overlaps the trough of another wave.Basically, the waves are cancelling out each other’s energy.
24Standing Waves http://youtu.be/NpEevfOU4Z8 http://youtu.be/uFwEGrxNp5Q If an incoming wave and a reflected wave have just the right frequency, they produce a combined wave that appears to be standing still even though it is really two waves interfering as they pass through each other.
25Nodes and Antinodes Node- a point of zero amplitude on a standing wave Antinode- a point of maximum amplitude on a standing wave
27Properties of WavesamplitudeWavelengthFrequencyspeed
28Amplitude- the greatest distance that the particles of the medium move from their rest positions
29In a transverse wave…The amplitude is a measure of the greatest distance up or down from the rest position.The larger the distance is from rest position to crest or from rest position to trough, the higher the energy of the wave.
30In a longitudinal wave… The amplitude is a measure of how compressed or rarefied the medium becomes.A high-energy wave causes more compression and rarefaction than a low energy wave. When the compressions are dense, it means that the wave’s amplitude is large.
31Wavelength- the distance between two corresponding parts of a wave crest to crest or trough to trough in a transverse wavecompression to compression in a longitudinal wave
32Frequency-the number of complete waves that pass a given point in a certain amount of time
34The faster the wave movement, the higher the frequency and the slower the wave movement, the lower the frequencyFrequency is measured in a unit called Hertz (Hz), named after the guy who discovered radio waves
35Speed Different waves travel at different speeds. For instance, which happens first during a thunderstorm—you see the lightning or you hear the thunder? Let’s take a look.
36Why do you see the light waves before you hear the sound waves? Because they travel at different speeds!Light travels about 1,000,000 times faster than sound!The speed of a wave is how far the wave travels in a given length of time.
37Speed=wavelength x frequency Time for some wave math!The formula used to relate speed, wavelength, and frequency of a wave is:Speed=wavelength x frequencyLet’s do some practice…
38What is the frequency?The speed of a wave on a rope is 50 cm/s and its wavelength is 10 cm.The speed of a sound wave through the air is340 m/s and the wavelength is 18 ft/s.*Hint: There are about 3 feet in a meter.
39What is the speed?A wave has a wavelength of 2 mm and a frequency of 3 Hz.A wave in a spring has a wavelength of 0.1m and a frequency of 20 Hz.
40What is the wavelength?A sound wave has a frequency of 660 Hz and its speed is 330 m/s.The speed of a wave on a guitar string is 142 m/s and the frequency is 110 Hz.