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……A MOVEMENT OF A MOVEMENT OF ENERGYENERGY
What are waves?
A wave is a movement of energy from a vibrating source outward A vibration – any movement that follows the same
path repeatedly Vibration = movement = energy
Waves carry energy from one place to another
Some waves need something to travel through…
Mechanical Waves Waves that require a medium to travel A medium is any form of matter (solid, liquid,
gas) The energy moves – not the medium Sound is one example of a mechanical wave
Some waves do not need something to travel through…
Electromagnetic Waves
Waves that do not require a medium Can travel with or without a medium Light, radio, x-rays, microwaves…..
Waves can be further classified by HOW THEY MOVE
TRANSVERSE WAVES
LONGITUDINAL WAVES
SURFACE WAVES
Transverse Waves
Waves that move the medium at right angles to the direction in which the wave is moving
Up and Down Light is a transverse
wave
LONGITUDINAL WAVES
Waves that move the medium parallel to the direction in which the wave is moving
Back and forth Sound is a longitudinal wave
SURFACE WAVES
A combination of Transverse and Longitudinal Occur between two mediums Up and down with a back and forth motion creates a circle
motion
Parts of a WaveParts of a Wave
All Waves have FOUR Basic Properties
Amplitude
Wavelength
Frequency
Speed
Amplitude
The maximum distance the particles of the medium carrying the wave move away from the rest position;
Corresponds to the amount of energy in the wave Higher amplitude = more energy
Wavelength The distance between
two corresponding parts of a wave
Shorter wavelength=more energy!
Crest to crest or Trough to trough
Compression to compression or rarefaction to rarefaction
Frequency
The number of complete waves that pass a given point in a certain amount of time;
Higher frequency=more energy
The number of vibrations in a second
Measured in the Hertz (Hz)
1 Hz = 1 wave per second
Speed
How far a wave travels in one unit of time Speed = wavelength x frequency
m/s = m x Hz (waves/sec)
The type of medium will affect wave speed For example, sound travels faster/slower in
different mediums; light travels through water at a different speed than through air
High Frequency, Low Amplitude
High Frequency, High Amplitude
Low Frequency, Low Amplitude
Low Frequency, High Amplitude
A wave with a high amplitude and a frequency of 1.5 Hz
2 sec
A wave with a low amplitude and a frequency of 5.5 Hz
1 sec
Wave Interactions
Waves interact with each other and their surroundings
Waves interact in FOUR basic ways
When an object or wave bounces back from a surface
None of the properties of a wave are changed by reflection. The wavelength, frequency, & speed are same before and after reflection. The only change is the direction in which the wave is traveling.
Reflecting Waves
Reflected light waves allow us to see things Reflected sound waves allow echoes to occur If something is not reflected, it may be
absorbed by or transmitted through the item
Reflection and sound
Echolocation
Sonar
Ultrasonography
When a wave bends due to a change in speed
When a wave moves from one medium to another at an angle, speed changes as it goes into different mediums
Due to change in speed, the wave bends
•When light waves are traveling through air, they have a certain speed;
•When they enter the glass, and then the water, their speed changes;
•To the right is an “overhead” view, showing that the wavelengths changed once the wave entered the new medium
When light enters a particular medium at When light enters a particular medium at an angle (or enters a prism) the wave will an angle (or enters a prism) the wave will change it’s change it’s speedspeed; speed depends upon ; speed depends upon wavelength, and since the colors that wavelength, and since the colors that make up light have different wavelengths, make up light have different wavelengths, they have different speeds and will then they have different speeds and will then be visible; be visible; Frequency did not change, that property Frequency did not change, that property depends upon the source, not the depends upon the source, not the medium.medium.
The bending of waves around the edge of a barrier
When a wave passes through or around a barrier it bends and spreads out
•Each of the dark lines represents a barrier that is “in the way of” the wave
•None of the properties of the wave are changed with diffraction;
•The wavelength, frequency and speed are the same before and after the diffraction;
•Again, like with reflection, the only change is in the direction of the wave
When two or more waves meet Constructive Interference
When two waves meet, combine, and create a wave with a larger amplitude Crest meets crest
Destructive Interference When two waves meet, combine, and create a wave with a smaller amplitude Crest meets Trough
Resonance
Standing waves – those that appear to be still; actually a wave and its reflection experiencing interference as they travel; this occurs a medium’s “resonant frequency.”
Resonance occurs when an object that is vibrating at or near another objects natural (resonant) frequency causes that other object/medium to vibrate
SOUND
Sound travels as a longitudinal wave Energy from a vibration is carried through the
medium as the molecules of the medium move back and forth as the disturbance goes by
You hear the sound when (and if) the disturbance reaches the medium near your ear
Speed of sound
The speed of sound is dependent upon the properties of the medium through which it travels; those properties include
Temperature Elasticity
Density
Temperature
Sound travels slower at lower temperatures
Sound travels faster at higher temperatures
Elasticity
Sound travels faster in a more elastic medium; Fastest in solids,
slowest in gases Speed of sound in
the ground is four times faster than in air!
Density
Density affects the speed of sound when considering mediums that are the same state or phase of matter
The less dense the medium, the faster the sound;
The more dense the medium, the slower the sound
Chuck Yeager
On October 14, 1947, Captain Chuck Yeager became the first person to fly a plane faster than the speed of sound.
How did Chuck Yeager “cheat” to break the sound barrier?
Speed of sound and the sonic boom "At sea level a plane must exceed 741
mph to break the sound barrier, or the speed at which sound travels. The change in pressure as the plane outruns all the pressure and sound waves in front of it is heard on the ground as an explosion or sonic boom. The pressure change condenses the water in the air as the jet passes these waves. Altitude, wind speed, humidity, the shape and trajectory of the plane - all of these affect the breaking of this barrier. The slightest drag or atmospheric pull on the plane shatters the vapor oval like fireworks as the plane passes through," he said. "You see this vapor flicker around the plane that gets bigger and bigger. You get this loud boom, and it's instantaneous. The vapor cloud is there, and then it's not there.”
Sonic Boom
What determines the sound you hear? Properties of sound include what you hear
and how high or low it sounds. Each of these is dependent upon the
properties of the wave producing the sound
Amplitude
The amplitude of a sound wave indicates the energy carried by the wave
The higher the amplitude, the more intense the sound, or the more loud the sound seems
Turn It Off!
The amplitude of sound, or its loudness, is measured in DECIBELs.
Environmental Noise
Weakest sound heard 0dB
Whisper Quiet Library 30dB
Normal conversation (3-5') 60-70dB
Telephone dial tone 80dB
City Traffic (inside car) 85dB
Train whistle at 500', Truck Traffic 90dB
Subway train at 200' 95dB
Level at which sustained exposure may result in hearing loss 90 - 95dB
Power mower at 3' 107dB
Snowmobile, Motorcycle 100dB
Power saw at 3' 110dB
Sandblasting, Loud Rock Concert 115dB
Pain begins 125dB
Pneumatic riveter at 4' 125dB
Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection
140dB
Jet engine at 100', Gun Blast 140dB
Death of hearing tissue 180dB
Loudest sound possible 194dB
Frequency
Frequency refers to the number of waves that pass a point in a second;
The frequency of sound waves indicates the pitch (how high or low) the sound has.
Frequency
The lower the frequency, the lower the pitch
700 Hz sound
The higher the frequency, the higher the pitch
1400 Hz sound
Turn It Off!
Draw a sound wave with a high pitch and low volume.
Draw a sound wave with a loud volume and a high pitch
Draw a sound wave with a low pitch and high volume.
Draw a sound wave with a low pitch and low volume.
The Doppler Effect
The apparent change in frequency as the wave source moves in relation to the listener
This is heard as a change in pitch
Assignment
Complete page 605 #’s 2-5 Read pages 606 – 611; add info to your
notes if necessary Complete page 611 #’s 3-5, 7-10