Transcript 8.1 Waves Notes

Chapter 8.1
Notes
Waves
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Wave motion is a
transfer of energy,
without the transfer of
matter.
A single disturbance in a
wave is called a wave
pulse.
Horn Bubble Demo
 Two
types of waves:
 Mechanical
 Electromagnetic
(will study in next
chapter)
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Mechanical waves require a
medium such as air, water, or
soil, to transfer the energy from
one place to another.
Examples of mechanical waves
include waves created by an
earthquake, waves created by
sound carried through the air,
and waves in a pond created by
a rock being thrown in.
Sound in a Vacuum
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A wave is created by a
vibration being passed
from one molecule to
another.
The molecules than
return to their original
position.
Vibration Demos
Music
Box
Singing Rod with Cup
Speaker with Mirror
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Electromagnetic waves
transfer energy also, but
they do not require a
medium (vacuum).
Example of an
electromagnetic wave is
light (can travel in the
vacuum of outer space)
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If a source makes a
single disturbance in a
wave it is called a single
pulse. If the source
vibrates repeatedly, it
produces a periodic
wave.
2 types of mechanical
waves include:

Transverse
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Longitudinal
Transverse vs Longitudinal
Demonstration
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In a transverse wave, the particles
in a medium move in a direction that
is perpendicular to the direction of
the wave motion. Example: a rope
being lifted up an down
In a longitudinal wave, the
particles in a medium move in the
same direction as the wave.
Example: a slinky being pushed and
pulled back and forth.
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The highest point on a
wave is called the peak or
the crest.
The lowest point on a wave
is called the trough.
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The distance from the rope’s
equilibrium to the crest is called the
amplitude.
The size of the amplitude of a wave
determines how much energy the
wave transfers.
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The length of the repeating pattern
is called the wavelength.
You measure the wavelength from
one crest to the next crest or from
one trough to the next trough.
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Frequency of a wave is the number
of waves that occur in a set amount
of time.
The Period of a wave is the amount
of time it takes for one complete
wavelength to pass a point.
Ruben’s Flame Demo
Frequency equation =
1/Period
 f = 1/T
 Period equation =
1/frequency
 T = 1/f
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 If
we have a frequency of 5
Hertz, what is the period?
 T = 1/f ; T = 1/5 = .2 s
 If we have a period of 1.3
seconds, what is the
frequency?
 f = 1/T ; f = 1/1.3 = .77 Hertz
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Not always given the
Period but instead given
cycles and time.
Frequency = number
of cycles / time
f = # of Cycles / t
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Using a stopwatch, you
determine that 3 waves pass a
boat every 6 seconds. What is
the frequency? What is the
period?
f = # of Cycles / t
f = 3 / 6 = .5
T = 1/f ; T = 1 / .5 = 2
Speed of a wave
equation =
wavelength x
frequency
 v =λf
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What is the speed of a
wave with a wavelength
of 2 feet and a
frequency of 5 Hz?
v =λf
V = 2 x 5 = 10ft/s
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A region where the wave is
pushed together in a
longitudinal wave is called
compression.
A region in a longitudinal
wave that is pulled apart is
called rarefaction.
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Sound is a longitudinal
wave.
The compression and
rarefraction of a
longitudinal wave is was
causes sound.