vibrations repetitive back and forth motions Waves a traveling disturbance that carries energy from one location to another Think about waves like ripples in a pond Mechanical Waves ID: 736504
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Slide1
Unit 4: Waves, Sound, and ColorSlide2
vibrations
- repetitive back and forth motions
Waves – a traveling
disturbance that carries energy from one location to another. Think about waves like ripples in a pond. Slide3
Mechanical Waves
Mechanical
waves – must travel through
matter.Matter = solids, liquids, and gases.CANNOT travel through a vacuum. Slide4
Electromagnetic Waves
Electromagnetic
waves – can travel through transparent material and vacuums.
Example? Light.Slide5
Longitudinal Waves
: compression waves
Transverse Waves
: sinusoidal wavesSlide6
Wave Terms!
Wavelength
(
λ) - the distance between two identical points on two consecutive waves.Frequency (f
) –
The number of oscillations, vibrations, or waves passing a reference point per second. We measure this in
hertz
(Hz).
Period
(T) – The time for one single oscillation, vibration, or wave.Wave Speed (c) – How fast a wave travels. Slide7
Note: Frequency and wavelength are inversely proportional to each other.
Greater frequency
shorter wavelength
Lower frequency greater wavelengthSlide8
Mechanical Waves
Energy begins moving via
disturbance
or vibration through an elastic source. Physical medium is needed.Energy transfers away
from the source.
It temporarily
changes
the medium.
Medium
goes back to the way it was after the wave has passed.The height of wave (amplitude) weakens the further it gets from the disturbance.Slide9
Stretch the spring using WORK against resistance, Create PE. If released, the spring will “snap back” to restore its original shape
Rest (equilibrium position): No motion, the shape of the spring is maintained by its restoring force.
Compress the spring using WORK against resistance, Create PE. If released, the spring will “snap back” to restore its original shape.
Energy relationship of a springSlide10
Stretch the spring to induce PE, then release!
Compressed position: v = 0, PE = 100%. Instantaneous change in direction.
Passing through the rest position (equilibrium position): v = max, PE = 0
Passing through the rest position (equilibrium position): v = max, PE = 0
Passing through the rest position (equilibrium position): v = max, PE = 0
Stretched position: v = 0, PE = 100%. Instantaneous change in direction
Simple harmonic motion of a springSlide11
Rest position
v = max, PE = 0
Max h: v = 0, PE = max
Instantaneous change in direction
Simple harmonic motion of a pendulum
Max h: v = 0, PE = max
Instantaneous change in directionSlide12
Simple harmonic motion of a standing wave (e.g., plucked string)
Rest position: v = max, PE = 0
Max displacement: v = 0, PE = max
Max displacement: v = 0, PE = maxSlide13
Air molecules become compressed at the condensations (increased pressure) and become diffused at the rarefactions (decreased pressure).Slide14
Human hearing range:
20-20,000
hertz
Sound travels fastest through solids and slowest through gases.Slide15
Why we care about waves for sound
amplitude
- the maximum displacement of the wave (or height of it).
Why we care: amplitude is the volumn of the sound. Rest - places where the wave has stopped and is sitting at equilibrium.
Why we care:
Pause
or
stop
in the music. Pause between notes.
Compressions = louderRarefactions = softer or quieter.Slide16
Reflection
- when a wave bounces off of something back toward you.
Why we care: This is how we
echo sound. Refraction - when a wave is bentWhy we care: this is what causes an changes.Slide17
Refraction tendencies
As sound waves pass through an air-solid boundary
Air
Glass: Speed up and change direction
Glass Air: Slow down and change direction
As sound waves pass through cold air-warm air boundary
Cold air
warm air: Speed up and change direction
Warm air cold air: Slow down and change direction
As sound waves pass through two different solids with different densities More dense
Less dense: Slow down and change direction Less dense More dense: Speed up and change directionSlide18
Intencity
of sound is measured in
pitch.
Anything over 80 decibels (dB) can cause permanent damage to your ears. Resonance – the vibration of sound left after the initial cause has been hit. Slide19
Beat
Beat
Beat
Beat
Noise
Noise
Noise
Noise
Wave 1
Wave 2
Wave functions are additive. Wave 1 and Wave 2 have different frequencies and wavelengths. When Wave 1 and Wave 2 interact, the sum of the waves will produce noise and beats. Noise is where individual waves are out of phase, thus produce non-harmonic multiple tones. Beat is where individual waves are in phase and the amplitudes combine to produce a harmonic pure tone.Slide20
Wavelengths and Sound
Wavelengths cause “notes.”
The
shorter the wavelength, the higher the sound. The longer the wavelength, the lower the sound. Slide21
Doppler Effect
The seeming change in
sound
because of the object’s or your movement.http://www.youtube.com/watch?v=z0EaoilzgGESound travels at the same speed but the objects or you
moves.Slide22
LIGHT
Light is
electromagnetic
waves, NOT longitudinal/compression. Slide23
Why we see
Our eyes have two main types of receptors:
rods
and cones.Rods- measure “lightness,” “darkness,” and register motion. cones- detect color. Slide24
Our cones have
3
color receptors in them. These are the three primary colors IN LIGHT.
RedBlueGreenSlide25
This is our color spectrum. We see all of this because of those 3 color cones.
Other animals have different cones, and can see other colors. Slide26Slide27
Animal Color Trivia
Dogs only have
2
color cones, so they can see shades of green, blue, and some yellows. Nocternal hunting animals can see into the infrared light spectrum. Bees can see into the ultraviolet spectrum, and scientists call that “bee yellow.” Butterflies have 5 different color cones in their compound eyes.
The mantis shrimp has 16. Slide28
More facts about the mantis shrimp
http://
theoatmeal.com/comics/mantis_shrimp
http://www.youtube.com/watch?v=F5FEj9U-CJMSlide29
Back to light
Light
reflects
and refracts.Reflection - we see reflection/color.Refraction - Bends light. This is why we don’t see things straight on in water. Slide30
When light bends through mist, it’s bending over and over again through thousands of
water droplets.
Every time it goes through a droplet, the light
changes.This makes us see the full color spectrum.In other words: a rainbow.Slide31
We see an object’s color because that’s the only color that object is
reflecting.
All the other color it absorbs.
WHITE – ALL color wavelengths reflected. BLACK – absence of color. NOTHING is reflected, EVERYTHING is absorbed. Slide32
Color Wheels
The Primary colors of light are red, blue, and green:
The primary colors when painting are red, blue, and yellow. Slide33
For painting: Primary colors are
red, yellow, blue.
Secondary colors are what they mix together to make:
green, purple, orange.Complementary colors are colors opposite on the color wheel. When mixed they make brown.Slide34