What Are Waves?
SMHS Engineering 2
Tatum
2013-2014
Link
Vibrations, Waves & Sound
Waves
The
Motion of Waves
Wave
Interference and
Energy
Investigation: Waves in Motion
Key Question:
How do waves move?
Objectives:
Explain how waves move.
Compare and contrast transverse and longitudinal waves.
Use knowledge of longitudinal and transverse waves to
describe water waves.
Waves
A
wave is an oscillation that travels from
one place to another.
If
you poke a floating ball, it oscillates up
and down.
The
oscillation spreads outward from where
it started.
Why learn about waves?
Waves
carry useful information
and energy.
Waves
—
—
—
—
are all around us:
light from the stoplight
ripples in a puddle of
electricity flowing in wires
radio and television and cell
phone transmissions
Recognizing waves around you
Waves
—
—
—
—
—
are present:
when you see a vibration that moves.
when something makes or responds
to sound.
when something makes or responds
to light.
when technology allows us to “see
through” objects.
when information travels through the
air (or space) without wires.
Waves
Waves
are a traveling form
of energy because they can
change motion.
Waves
also carry
information, such as sound,
pictures, or even numbers.
Wave pulses
A
It
wave pulse is a short ‘burst’ of a traveling wave.
is sometimes easier to see the motion of wave
pulses than it is to see long waves with many
oscillations.
Transverse waves
A
transverse wave has its oscillations
perpendicular to the direction the wave moves.
A
wave pulse along a rope attached to a wall moves
left to right, while the boys hand moves up and
down.
Longitudinal waves
The
oscillations of a longitudinal wave are in the
same direction that the wave moves.
Longitudinal waves
A sharp push-pull on the
end of the spring results in a
traveling wave pulse as
portions of the spring
compress, then relax.
Sound waves are
longitudinal waves.
Like a wave pulse on a
spring, air molecules
oscillate back and forth as
sound travels.
Frequency, amplitude, and wavelength
You
can think of a wave as a moving series of
high points and low points.
A crest is the high point of the wave.
A trough is the low point.
Frequency
The
frequency of a wave is the rate at which
every point on the wave moves up and down.
Frequency
means “how often”.
Amplitude
The
amplitude of a water wave is the maximum
height the wave rises above the level surface.
Wavelength
Wavelength
is the distance from any point on a
wave to the same point on the next cycle of the
wave.
The
distance between one crest and the next
crest is a wavelength.
The speed of waves
The
speed of a water wave is how fast the wave
spreads, NOT how fast the water surface moves
up and down or how fast the dropped ball moves
in the water.
How do we measure the wave speed?
The speed of waves
A
wave moves one
wavelength in each cycle.
Since
a cycle takes one
period, the speed of the
wave is the wavelength
divided by the period.
The speed of waves
The
speed is the distance traveled (one
wavelength) divided by the time it takes (one
period).
We
usually calculate the speed of a wave by
multiplying wavelength by frequency.
Calculating wave speed
A wave has a wavelength of 0.5 meters, and its frequency is
40 hertz. What is the speed of the wave?
1.
Looking for: …speed of the wave.
2.
Given: …wavelength (0.5 m) and frequency (40 Hz).
3.
Relationships: Use formula: speed = ƒ x λ
4.
Solution: …speed = 40 Hz × 0.5 m = 40 1/s × 0.5 m
speed = 20 m/s