Characteristics Of Mechanical Waves

Chapter 10
Section 1:

Wave- a repeating disturbance or movement that transfer energy through matter of space.
EX: water, light, sound, seismic (earthquakes), and electromagnetic (ultraviolet, radio, infrared, microwaves, x-ray)
Characteristics of Waves:
Produced by something that vibrates
Carry energy without transporting matter from place to place
Will travel only as long as it has energy to carry
The larger the wave- the more energy it carries and energy can spread out as the wave travels away from the source
Mechanical Waves
Waves that can travel only through matter
Medium- the matter waves travel through
A medium can be a solid, liquid, or gas, or combination
EX: A) drop a rock in a lake-water is medium
B) Sound- air is the medium
C) Earthquake (seismic)- earth is medium
Not all waves need a medium- some can travel through space (such as light and radio waves)
Two Types of Mechanical Waves
1) Transverse Waves
2) Compressional or longitudinal Waves
Particles (matter) in a wave can vibrate up and down or back and forth
Transverse Waves
Matter in the medium moves back and forth at right angles to the direction that the wave travel (crosswise)
EX: light waves, wave in a rope, people in a crowd at a sporting event
Compression Waves
Matter in the medium moves back and forth along the same direction that the wave travels (parallel to the wave direction)
EX: stretching out a slinky, sound waves
Some waves are a combination of the two types of waves

Surface Waves
Matter that moves in a circle
EX: water/ocean waves
Water Waves
Water moves back and forth as well as up and down causing it to move in circles
Ocean waves are formed most often by wind blowing across the surface. As the wind blows- it is like a vibration
The size of the waves depend on:
Wind speed
Distance the wind blows
How long the wind blows
Seismic Waves
A combination of transverse and compressional waves
When Earth’s crust shifts, or breaks, the energy that is released is transmitted outward, causing an earthquake
When objects on Earth’s surface absorb some of the energy carried by seismic waves, they move and shake.
The more the crust moves during an earthquake, the more energy is released
Sound Waves
Are compressional waves
Air is medium- when a noise is made, air molecules push together by the vibrations
Other materials as a medium (such as water or wood) –particles in these mediums are pushed together and move apart as sound waves travel through them
Sound travels faster in solids; slowest in gases
When a sound wave reaches your ear:
It causes your ear drum to vibrate
Your inner ear then sends signals to your brain
Your brain interprets the signals as sound

Section 2
Wave Prosperities
Crest- highest points
Through- lowest points
Amplitude- maximum distance that wave reaches from resting position
Rest = crest
Rest = trough
The amplitude indicates the amount of energy carries by the wave
Wavelength
Distance between two consecutive crest or troughs (crest to crest or trough to trough)
Symbol is the Greek letter lambda
Measured in meters

Wavelength for Compressional Wave:
Distance between two consecutive compression or rarefactions (compression to compression or rarefaction to rarefaction)
Compression- region where the medium becomes crowded together (more dense)
Rarefaction- the less-dense region of a compressional wave
The Period of a wave:
The amount of time it takes one wavelength to pass a certain point
(Measured in seconds)
Frequency
The number of waves that pass a certain point in a given amount of time
Symbol is F
(Unit) Measured in hertz (Hz)
As frequency increases, wavelength decreases
A frequency of 1 Hz means that one wavelength passes in 1sec
In SI units, 1 Hz is the same as 1/sec
Speed
The speed of a wave is determined by the number of waves passing a point in a certain amount of time and the length of the wave

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