Waves Notes
Intro to Waves






























A wave is a disturbance that moves energy from one place to another.
Mechanical waves need a medium to pass through in order to move.
A medium is a substance the wave travels through.
Electromagnetic waves do Not need a medium to travel from place to place.
Waves do not move the material they travel through; they vibrate the material they travel
through.
Energy causes one particle to bump into the next particle and so on down the line and this is
how the energy is moved from place to place.
Falling dominoes is an example of how energy is transferred, but the material doesn’t move
A source of energy is always needed to cause a wave.
A vibration is repeated up and down or back in forth movement.
There are two types of waves, transverse and longitudinal.
Transverse waves are like ocean waves, they move up and down or back and forth.
The top of the wave is called the crest and the bottom is called the trough.
Longitudinal waves compress and expand like an accordion.
Sound waves are an example of longitudinal waves.
Properties of Waves
Amplitude is how high above or how low below the resting point a wave moves.
The greater the energy the greater the amplitude. Ex. The stronger the wind the higher the
ocean wave.
Wavelength is the distance from crest to crest or trough to trough in between two waves.
Frequency how many waves pass a specific point in a given amount of time.
Frequency is measured in units called hertz.
1 hertz is one wave in one second.
A kilohertz is 1,000 waves per second
A megahertz is 1 million waves per second.
Speed of a wave is wavelength X frequency.
Frequency equals speed divided by wavelength
Wavelength equals speed divided by frequency.
Interaction of Waves
Reflection is when a wave hits a surface and bounces off because it cannot pass through.
Refraction is the bending of a wave due to a change in its speed. Ex. Is when a wave goes from
air to water.
Refraction only occurs if the wave enters the new medium at an angle.
Diffraction happens when a wave moves around a barrier or through an opening and then
bends or spreads out. Ex. sound waves coming through a door.
Resonance is an increase in the amplitude of a natural vibration that occurs in an object. Ex. is
when a stringed instrument has a better sound.
ELECTROMAGNETIC WAVES







Contain both electricity and magnetic fields
Move at the speed of light
Do not need a medium to pass through
Come from the sun
Have different wavelengths and different frequencies
The electromagnetic spectrum is made up of all electromagnetic waves in order of
increasing frequencies ( energy)
Range- Radio waves, microwaves, infrared waves, visible light, ultraviolet waves, x-rays,
gamma rays.
RADIO WAVES
 Have the longest wavelength and the lowest energy
 Radio waves with the highest amount of energy are microwaves.
 Cell phones and radar guns are examples
INFRARED



Heat rays
Examples are heat lamps in restaurants
Infrared cameras (night vision goggles)
VISIBLE LIGHT


Longest wavelength is red
Shortest wavelength is violet
ULTRAVIOLET RAYS



Have enough energy to kill cells
Cause you to produce vitamin D
Causes sunburn and skin cancer
X-RAYS


Can pass through skin and soft tissue, but is absorbed by teeth and bone
Too much exposure can cause cells to die
GAMMA RAYS









Electromagnetic waves with the most energy
Used to kill cancer cells
The radiation released from nuclear power plants and nuclear bombs.
Seismic Waves
Seismic waves are waves produced by earthquakes.
Seismic waves come in two types, S waves and P waves.
P waves or primary waves are longitudinal waves.
These are the fastest seismic waves.
S waves or secondary waves are transverse waves.
S waves cannot pass through liquids so they cannot pass through the center of the earth.


Surface waves are P and S waves that reach the earth’s surface.
A seismograph is the tool scientist use to measure an earthquakes strength and location.
Sound Waves

















Sound always begins with a vibration.
When sound waves reflect off a surface you sometimes hear an echo.
Sound waves diffract or bend around objects and through openings. Ex. why you can hear
someone talking in the hall.
The speed sound travels depends on variables such as elasticity, density, and the temperature of
the object the sound is passing through.
Elasticity is how fast a particle bounces back to its original position after being vibrated.
When the state of matter is the same the material that is less dense allows the sound to travel
faster.
The higher the temperature the faster sound travels.
Sound travels through air at around 760 mph at a temperature of approximately 70 degrees.
Sound travels through ocean water at 3,400 mph when the water is around 75 degrees
Sound travels through glass at 11,500 mph when the temperature is approximately 85 degrees.
Two factors determine the loudness of a sound. The energy to make the sound and the distance
from the sound.
A decibel is the unit we use to measure sound.
20 decibels is a whisper and a jack hammer is 120 decibels.
Pitch is how high or low a sound appears to a person
The higher the frequency the higher the pitch of a sound.
People can hear sounds between 20 and20,000 hertz.
One can change the pitch of an object by making it vibrate faster.