Waves
What is a wave?


Repeating disturbance that transfers energy through matter or
space
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Waves in water
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Sound

Light
When traveling through matter, they are caused by particles
transferring energy to other particles
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The wave does not “move”
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
It transfers energy causing particles around it to move
Waves carry energy without transporting matter
Making Waves
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Waves only travel as long as they have energy
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As the energy is lost, the waves decrease in size
All waves are due to vibrations
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Movement up and down, or back and forth
Mechanical Waves
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Waves that can only travel through a medium
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Medium=matter through which a wave travels
Sound waves, water waves, and other waves we can see are
mechanical waves
Transverse waves

A wave where particles in the medium move back and forth at right
angles to the direction of the wave
Longitudinal waves

Waves in which the particles move back and forth
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Same direction as the movement of the wave
Most of the waves we cannot see

Sound waves
Seismic Waves
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Caused by the movement of Earth’s Crust
Properties of Waves
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Parts of a wave
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Transverse waves:
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Crest-high points
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Trough-Low points
Longitudinal waves:
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Compression- more dense region
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Rarefaction- less-dense region
Wavelength
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The distance between one part of the wave, and the next just like it
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Represented by Greek letter lambda (λ)
Frequency and Period

Frequency-number of wavelengths that pass a fixed point each second

Measured in Hertz (Hz)
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1 Hz= 1/s
Related to frequency
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Longer wavelengths have longer frequencies

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More small waves pass through a point than longer waves
Period

Amount of time it takes one wavelength to pass a point in seconds
Wave Speed

The speed of a wave depends on the medium through which it
travels



More particles in a liquid

Exception: Light travels more slowly in liquids than gases
Changes to the medium can affect the wave’s speed


Usually faster in liquids than gases
Sound travels quicker at warm temperatures than in cool temperatures
Equation:

𝑣 = 𝑓𝜆
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Speed=frequency x wavelength
Practice Problem

If a wave has a frequency of 5 Hz, and a wavelength of 2 m, what is
the speed of the wave?
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10 m/s
Practice #2

What is the wavelength of a wave with a frequency of 4 Hz traveling
at 16 m/s?
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4m
Challange

The speed of light is about 3x108 m/s. If a light wave has a
wavelength of 3 m, how many waves will pass a certain point in 1
second?

100,000,000
Amplitude

Measure of the size of the disturbance of a wave


In longitudinal waves,
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High-amplitude waves have compressions closer together and rarefactions
farther apart
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Low-amplitude waves have compressions further apart and rarefactions
closer together
In transverse waves,
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From the rest position to the crest or trough
Reflection
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Occurs when a wave strikes an object and bounces off of it
The Law of Reflection
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Beam hitting the object is the incident ray
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The reflected beam is the reflected ray
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The perpendicular line between them is the
normal

i is the angle of incidence
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r is the angle of reflection

The Law of reflection states that i and r are
equal
Practice

A laser hits a mirror at 25 degrees to the normal. What will be the
angle of reflection to the normal?
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25 degrees
You try it

A beam of light hits a mirror at an angle of 10 degrees from the
mirror. What is the angle of reflection from the normal?
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80 degrees
Refraction
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Bending of waves due to change in speed from one medium to
another
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When light slows down, it bends toward the normal

When light speeds up, it bends away from the normal
Diffraction

The bending of waves around an object
Interference
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Multiple waves overlap and combine to form a new wave
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Constructive interference: Waves add together
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Destructive interference: Waves subtract from one another
Standing Waves

Occurs when waves equal in wavelength and amplitude, but in
opposite directions, constantly interfere with each other
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https://www.youtube.com/watch?v=no7ZPPqtZEg
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The waves appear not to move
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Standing waves have nodes

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Places where interfering waves always cancel
Used in instruments to produce pure sounds
Resonance

Process by which an object is made to vibrate by absorbing energy
at its natural frequency


Swinging on a swing (have to pump at the right time to speed up)
https://www.youtube.com/watch?v=wvJAgrUBF4w