7th grade Notes Week 17Monday
Waves Intro
Waves Intro:
what it is…
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A wave is a
disturbance caused
by a force
Example: you drop
a pebble in water, a
wave is formed
Waves: What do they do?
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Waves transfer
ENERGY
The molecules of the
MEDIUM do NOT
Move to another place…
Waves Intro: Causes &
Examples
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a)Water waves…caused
by wind (some by
Earthquakes- tsunami)
b)Ground shakes
because pressure is
released
(EARTHQUAKE)
c)You hit something it
vibrates making a
sound. Sound moves in
waves
Waves Intro:
Types of waves
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There are two
types of waves:
Mechanical and
Electromagnetic
Waves Intro:
Mechanical
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Mechanical waves are
waves that move in
MATTER.
If there is no
“MATTER”; there is no
movement
MEDIUM- is any type of
matter that mechanical
waves move in
Mechanical Wave:
An example
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•Sound is an example
of a mechanical wave.
•Sound is produced
by vibrations
•The energy from the
vibration moves in
waves
•Sound can ONLY
travel if there is a
medium
Waves Intro:
Electromagnetic
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Electromagnetic
waves can move
through “empty”
space.
A place with little
or no molecules is
called a vacuum
Parts of a Transverse
wave
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Crest- highest
point of the
wave
REST LINE
If there were no energy…
Trough (troff)lowest point of the
wave
Types of mechanical
waves
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Transverse waves are
waves in which the
movement of the
vibrating particles is
perpendicular to the
direction of the wave.
Example:
Water wave
Types of mechanical
waves
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Longitudinal waves are
waves in which the
movement of the
vibrating particles is
parallel to the direction
of the wave.
Example: sound wave
Frequency:
How many crests
pass in a second
Amplitude:
Measure
from rest
line to crest
Wavelength:
Measure from one
crest to the next
Properties of (ALL) Waves
Amplitude
What does it
measure?
The energy of
the wave.
The more
amplitude the
more energy.
Diagram of
what it
measures
Wavelength
What does it
measure?
Frequency
What does it
measure?
The distance
between one
crest and
another
The number of
vibrations
(waves) each
second.
Unit used: hertz
Diagram of
what it
measures
Diagram of
what it
measures
Sound Energy
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Sound energy is the
energy of vibration
Sound produces an
mechanical wave- it
needs a medium to
move in
Sound Energy
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Sound waves are
LONGITUDINAL
waves
Another name for
longitudinal waves
is a COMPRESSION
wave
Sound Energy
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Sound waves have the
same properties as
waves (amplitude,
wavelength,
frequency)
However there are two
“parts” to a
COMPRESSION wave
Sound Energy
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Compression- where
molecules of medium
and pressed together
Rarefaction- where
molecules of a medium
spread apart
Hearing and Wave
properties
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Our ears can sense
the amplitude of a
sound wave
The more energy,
the more amplitude.
Hearing and Wave
properties
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The greater
amplitude is sensed
as INTENSITY
(LOUDNESS)
The sound intensity
is measured with a
unit called decibel
Hearing and Wave
properties
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Our ears can sense
frequency of the
vibration
The more
vibrations, the
higher the
frequency. This is a
high pitch sound
Hearing and Wave
properties
C-notes
Our ears can sense
frequency of the
vibration
The more
vibrations, the
higher the
frequency. This is a
high pitch sound
Hearing and Wave
properties
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Frequency is
measured in a unit
called HERTZ (Hz).
These are vibrations
per second
We can “hear” 20
hertz to 20,000
hertz