©Sound
waves,
©visible
light waves,
©radio
waves,
©microwaves,
©water
waves,
©sine
waves,
©telephone
chord waves,
©stadium
waves,
©earthquake
waves,
©waves
on a string,
©slinky
waves
Definition of wave
a wave is the motion of a
disturbance.
©Let’s
use a slinky wave as an example.
©When
the slinky is stretched from end to end and is held at rest, it assumes a
natural position known as the equilibrium or rest position.
©To
introduce a wave here we must first create a disturbance.
©We
must move a particle away from its rest position
©One way to do this is to jerk the
slinky forward
©the beginning of the slinky moves
away from its equilibrium position and then back.
©the disturbance continues down
the slinky.
©this disturbance that moves down
the slinky is called a pulse.
©if we keep “pulsing” the slinky
back and forth, we could get a repeating disturbance.
©This
disturbance would look something like this
©This
type of wave is called a LONGITUDINAL
wave.
©The
pulse is transferred through the medium of the slinky, but the slinky itself
does not actually move.
©It
just displaces from its rest position and then returns to it.
©So
what really is being transferred?
©Energy
is being transferred.
©The metal of the slinky is the
MEDIUM in that transfers the energy pulse of the wave.
©The medium ends up in the same
place as it started … it just gets disturbed and then returns to it rest
position.
©The same can be seen with a
stadium wave.
©The wave we see here is a
longitudinal wave.
©The medium particles vibrate
parallel to the motion of the pulse.
©This is the same type of wave
that we use to transfer sound.
©Can you figure out how??
©A second type of wave is a TRANSVERSE wave.
©We said in a longitudinal wave
the pulse travels in a direction parallel to the disturbance.
©In a transverse wave the pulse
travels perpendicular to the disturbance.
©The differences between the two
can be seen
©Transverse
waves occur when we wiggle the slinky back and forth.
©They
also occur when the source disturbance follows a periodic motion.
©A
spring or a pendulum can accomplish this.
©The
wave formed here is a SINE wave.
Anatomy
of a Wave
Wave
frequency
©We know that frequency measure
how often something happens over a certain amount of time.
©We can measure how many times a
pulse passes a fixed point over a given amount of time, and this will give us
the frequency.
©Suppose I wiggle a slinky back
and forth, and count that 6 waves pass a point in 2 seconds. What would the frequency be?
©3
cycles / second
©3
Hz
©we
use the term Hertz (Hz) to stand for cycles per second.
Wave
Period
©The
period describes the same thing as it did with a pendulum.
©It
is the time it takes for one cycle to complete.
©It
also is the reciprocal of the frequency.
©T
= 1 / f
©f
= 1 / T
Wave
Speed
©We
can use what we know to determine how fast a wave is moving.
©What
is the formula for velocity?
©velocity = distance / time
©What
distance do we know about a wave
©wavelength
©and
what time do we know
©period
©so if we plug these in we get
©velocity = length of pulse / time for pulse to move pass a fixed point
©v = l / T
©we
will use the symbol l to represent wavelength
©v = l / T
©but
what does T equal
©T = 1 / f
©so
we can also write
©v = f l
©velocity = frequency * wavelength
©This is known as the wave equation.
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