 # Chapter 14 Waves.

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Chapter 14 Waves

Waves carry energy without transporting matter
a repeating disturbance or movement that transfers energy through matter or space A rhythmic disturbance that carries energy through matter or space. Molecules pass energy on to neighboring molecules Waves carry energy without transporting matter All waves are produced by something that vibrates Medium - material which a wave travels thru May be solid, liquid, or gas Not all waves need a medium to travel through Example: Light waves Wave Pulse A single bump or disturbance that travels through a medium

Longitudinal or Compressional waves
Mechanical waves waves that can travel only through matter Transverse waves matter in the medium moves back and forth at right angles to the direction that the wave travels. Example: Water waves Longitudinal or Compressional waves matter in the medium moves in the same direction that the wave travels. Example: Sound waves Surface Waves Combination of both transverse or compressional examples: water waves, seismic waves

Transverse waves have crests & troughs
Ways waves differ 1. How much energy they carry 2. How fast they travel 3. How they look Transverse waves have crests & troughs Crest —the highest points Troughs—the lowest points. Compressions Dense regions of compressional waves Rarefactions Less dense regions of compressional waves

Wavelength (λ) Frequency (f)
the distance between one point in the wave and the nearest point just like it Frequency (f) how many wavelengths pass a fixed point each second Expressed in hertz (Hz) As frequency increases, wavelength decreases. The frequency of a wave equals the rate of vibration of the source that creates it.

velocity = wavelength * frequency Speed of a wave = v = λ*f
Wave velocity, v describes how fast wave moves forward velocity = wavelength * frequency Speed of a wave = v = λ*f f = 1/T = 1/period Light waves travel faster than sound waves Sound waves travel faster in liquids and solids than in gas Light waves travel faster in gases and empty space than in liquids & solids

Amplitude of transverse waves
a measure of the energy in a wave More energy a wave carries, the greater its amplitude. Amplitude of compressional waves is related to how tightly the medium is pushed together at the compression The denser the compressions, the larger the amplitude is and the more energy the wave carries The less dense the rarefactions, the larger the amplitude and the more energy the wave carries Amplitude of transverse waves The distance from the crest or trough of a wave to the normal position of the medium Ex. how high ocean wave appears above water level

Reflection occurs when a wave strikes an object and bounces off of it.
All types of waves can be reflected. The angle of incidence always equals the angle of reflection Normal An imaginary line that is perpendicular to reflective surface

Incidence Wave Angle of incidence Angle of reflection Refraction
The wave that strikes the boundary Angle of incidence the angle formed by the wave striking the surface and the normal Angle of reflection angle formed by reflected wave and normal Refraction bending of a wave caused by a change in its speed as it moves from 1 medium to another

The greater the change in speed is, the more the wave bends.
When a wave passes into a material that slows it down, the wave is bent toward the normal. When a wave passes into a material that speeds it up, the wave is bent away from the normal. Diffraction an object causes a wave to change direction and bend around it If obstacle is smaller than wavelength, wave diffracts a lot If obstacle is larger than wavelength, wave does not diffract much The larger the obstacle is compared to the wavelength, the less the waves will diffract

Constructive interference Destructive interference
ability of two or more waves to combine & form a new wave Waves pass thru each other & continue in original direction New wave exists only while original waves are overlapping Constructive interference waves add together Destructive interference waves subtract from each other

Standing waves Nodes Resonance a wave pattern that stays in one place
Form when waves of equal wavelength & amplitude that are traveling in opposite directions continuously interfere with each other Nodes the places where two waves always cancel each other Resonance ability of an object to vibrate by absorbing energy at its natural frequency