17.1 Mechanical Waves
In a wave pool, the waves carry energy across the pool. You can see the effects of a wave's energy when the wave lifts people in the water.
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What Are Mechanical Waves?
What causes mechanical waves?
A mechanical wave is created when a source of energy causes a vibration to travel through a medium (substance).
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What Are Mechanical Waves?
A mechanical wave is a disturbance in matter that carries energy from one place to another.
The material through which a wave travels is called a medium.
Solids, liquids, and gases all can act as mediums. A vibration is a repeating back­and­forth motion. 3
Types of Mechanical Waves
The three main types of waves:
1. Transverse
2. Longitudinal
3. Surface Waves
They are classified by the wave they move through a medium.
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Transverse Waves
The medium vibrates perpendicular to the direction of the wave. Direction of wave
Crest
Rest position
Direction of vibration
Trough
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Types of Mechanical Waves
>
>
Transverse Waves
When you shake one end of a rope up and down, the vibration causes a wave.
>
>
The highest point of the wave is the crest.
The lowest point of the wave is the trough.
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Longitudinal Waves
In a slinky, the wave carries energy along the spring. ­The particles spaced close together are called a compression. ­An area where the particles in a medium are spread out is called a rarefaction.
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Longitudinal Waves
A longitudinal wave is a wave in which the vibration of the medium is parallel to the direction the wave travels.
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Surface Waves
A surface wave is a wave that travels along a surface separating two media.
ex: ocean waves
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Surface Wave
Wave direction As the ocean wave moves to the right, the bobber moves in a circle, returning to its original position.
> When a crest passes the bobber, the bobber moves up. When a trough passes, the bobber moves down. > The bobber also is pushed back and forth by the surface wave, like the motion of a longitudinal wave.
> The two motions combine, and the bobber moves in a circle.
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17.2 Properties of Waves
Frequency- the number of complete cycles in a give time.
1 Hertz (Hz)= 1 cycle per second
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Wavelength- distance between a point on one wave and the same point on
the next wave.
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Amplitude- maximum displacement of the medium from its rest position.
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line of origin/
rest point
trough
amplitude
crest
wavelength
frequency-how
often a wave
passes through a
medium
period-amount of
time it takes 1
wave to pass
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wave #
crest
trough
wavelength
1
1cm
1cm
2cm
2
3.5cm
3.5cm
2.5cm
3
.5cm
.5cm
3cm
4
2cm
2cm
.5cm
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Wave Speed= wavelength X frequency
One end of a rope is vibrated to produce a wave with a wavelength of
0.25 meters. The frequency of the wave is 3.0 hertz. What is the
speed of the wave?
= WAVELENGTH
Wavelength= 0.25 meters
Frequency= 3.0 Hz
f
=FREQUENCY
Speed= 0.25X 3.0
= 0.75 m/s
A wave on a rope has a wavelength of 2.0m and a frequency of 2.0 Hz. What is
the speed of the wave?
Speed= 2.0x2.0
=4.0 m/s
What is the wavelength of an earthquake wave if
it has a speed of 5km/s and a frequency of 10Hz
Speed= wavelength x frequency
5km/s= wavelength x 10Hz
wavelength= 0.5 km
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Assignment:
Waves problems #1 (blue worksheet)
SHOW ALL OF YOUR WORK!!!!!!
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