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Introduction to
Waves
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A wave is a traveling disturbance that travels through space
and matter transferring energy from one place to another.
Waves it transfer energy, not matter.
Mechanical waves are waves that require a medium. This
means that they have to have some sort of matter to travel
through. These waves travel when molecules in the medium
collide with each other passing on energy. One example of a
mechanical wave is sound. Sound can travel through air, water,
or solids, but it can't travel through a vacuum. It needs the
medium to help it travel. Other examples include water waves,
seismic waves, and waves traveling through a spring.
Electromagnetic waves are waves that can travel through a
vacuum (empty space). They don't need a medium or matter.
They travel through electrical and magnetic fields that are
generated by charged particles. Examples of electromagnetic
waves include light, microwaves, radio waves, and X-rays.
Basic wave
properties:
Example: Light
crest
amplitude
wavelength
trough
Parts of a Longitudinal Wave
Compression
Rarefaction
Example: Sound
Waves carry energy
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Amplitude describes the loudness of a sound and the
amount of energy the wave is carrying.
Amplitude is independent of wavelength, frequency
and speed.
Amplitude is independent of wave length,
frequency, and period.
How can we prove
the tuning fork is
carrying energy?
Longitudinal Wave vs. Transverse Wave
Sound waves are
longitudinal or
compressional waves
because oscillations occur
in the same direction that
the energy travels.
Transverse waves have
oscillations perpendicular to
their direction of motion.
Frequency is the amount of waves that
pass a point in a given amount of time.
Number of waves
Frequency 
Time
Frequency (Hz) vs. Period (seconds)
Determine the Frequency and Period of the following waves.
f1 = 20 Hz
T1 = 0.05 s
f2 = 30 Hz T1 = 0.033 s
1
T
f
If we know the frequency of a wave and the
length of the wave, we can find its velocity.
velocity = frequency x wavelength
l = 2m
Wave Equation
v  fl
f  3 Hz
velocity = 2 m x 3 waves/second = 6 m/s
1. A wave with a frequency of 14 Hz has a wavelength of
3 meters. At what speed will this wave travel?
2. The speed of a wave is 65 m/sec. If the wavelength of
the wave is 0.8 meters, what is the frequency of the wave?
How fast does sound move?
340 meters
Sound travels approximately 340 m/s through the air. It will
travel faster through a medium with molecules closer together.
For example, a solid concrete wall.
Sound travels at 1440 m/s in water where the molecules are
closer together.
Solid
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Gas
How does a sound wave
move?
Your voice, an instrument
or anything moving back
and forth causes a
vibration here.
The vibration travels
through the air as a series
of compressed molecules
and separated molecules.
Sound needs a medium (“stuff”) to travel through.
Sound waves cannot travel in a vacuum.
Would you really hear
spaceships fighting in
outer space? Why or why
not?