# Ch. 20 Wave Notes Cool Wave Effect Cool Wave Effect.

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Ch. 20 Wave Notes Cool Wave Effect Cool Wave Effect

A. How are Waves Described ? 1. Introduction: (Video) (Video) a) Wave= any disturbance that transmits energy through matter or space b) Waves carry energy– but the material through which the wave travels does not move w/ the energy- The Matter Vibrates! 1. A medium - substance through which a wave can travel (can be solid, liquid, or gas) 2. Mechanical wave = require a medium (Ex. Sound) 3. Electromagnetic wave = can travel through a vacuum and do not require a medium (Ex. Visible Light)

2. How are waves classified based on disturbance of the medium they travel through? (based on direction of the particles move as they vibrate compared w/ direction in which the waves travel) a. Transverse waves vibrate the particles of the medium w/ an up and down motion, causing the energy to move across or perpendicular to that wave. Video Video Crest = top of the wave Crest = top of the wave Trough = bottom of the wave Trough = bottom of the wave Ex: electromagnetic waves Ex: electromagnetic waves crest trough

b. Longitudinal waves - waves that vibrate the particles of the medium back and forth, causing the energy to move parallel to the wave Video Video Compression - section where the particles are crowded together Compression - section where the particles are crowded together Rarefraction - section where the particles aren’t crowded together Rarefraction - section where the particles aren’t crowded together Ex: sound wave Video Video Compression Rarefaction

c. Surface Wave = Combination of waves that occur at or near the boundary between two media, a transverse wave and a longitudinal wave can combine Video-Surface Wave Video-Surface WaveVideo-Surface Wave Wave Animations Link

B. What are the Properties of Waves? Video Video 1. Amplitude is the maximum distance the wave vibrates from its rest position. The larger the amplitude the more energy the wave has and the taller the wave. 2.Wavelength - distance between any two adjacent crest and compressions in a series of waves. Shorter λ has higher E than long λ. Symbol= λ 3. Frequency= the number of waves produced in a given amount of time. Measured by counting the number of waves that pass in a certain amount of time. Expressed in Hertz (Hz); one Hertz= one wave per second. High Frequency carries more energy. 4. Wave speed= the speed in which a wave travels. Formula: wave speed (v)= wave length (λ) x frequency (f) V= λ x f The distance a single crest/ compression travels in a given time The distance a single crest/ compression travels in a given time Depends on medium Video: Simulation Depends on medium Video: SimulationVideo: SimulationVideo: Simulation

Larger Amplitude Means More Energy What does changing amplitude do to a sound wave? What does this do to EM Wave (light)?

Which sound wave has the lowest pitch (f)? Highest pitch (f)?

Which color light has the highest frequency? Which color light has the highest frequency?

C. How do waves interact? 1. Reflection: when a wave bounces back after striking a barrier Ex: water, sound, and light waves reflect Ex: water, sound, and light waves reflect Video 2. Refraction: the bending of a wave as it passes at an angle from one medium to another because the wave is changing speed as it enters another medium… therefore it depends on a medium Video Reflection Refraction Mirror

d. Diffraction: the bending of waves around a barrier or through an opening Video

4. Interference: when two or more waves share the same space; they overlap. a. Constructive interference occurs when the crests of one wave overlap the crests of another wave(s). When the waves overlap, a new wave is created with a larger amplitude.

b. Destructive Interference- occurs when the crests of one wave and the troughs of another wave overlap. The resulting wave has smaller amplitude. Video Animation

c. Standing wave certain parts of the wave remain standing (called nodes and antinodes). The result is that the wave appears to be standing still which is the result of 2 identical waves traveling in opposite directions. The result is that the wave appears to be standing still which is the result of 2 identical waves traveling in opposite directions. Video Video Video

Examples of Standing waves: A= Antinode N= Node Remember: V= f x λ As frequency increases then the wavelength decreases. As frequency increases the ENERGY increases As frequency increases the amplitude increases

5. Resonance means resound or sound again. All objects have a natural frequency. All objects have a natural frequency. When an object is disturbed it will vibrate at its own special set of frequencies, producing a unique sound. When an object is disturbed it will vibrate at its own special set of frequencies, producing a unique sound. Occurs when the vibration of an object matches another object’s natural frequency causing it to vibrate. Occurs when the vibration of an object matches another object’s natural frequency causing it to vibrate. The 2 objects vibrate together and an increase in the amplitude occurs. The 2 objects vibrate together and an increase in the amplitude occurs. o Ex: Tacoma Narrows Bridge Disaster, musical instruments o Tacoma Narrows Bridge Video Tacoma Narrows Bridge Video Tacoma Narrows Bridge Video o Wine Glass Video Wine Glass Video Wine Glass Video o Wine Goblet Resonance Wine Goblet Resonance Wine Goblet Resonance

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