Download Waves

Waves
Catch it!
Wave Joke
• The Physicist, upon seeing all the waves, gets
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very excited and runs into the water,
disappearing.
The Marine Biologist, aware of tremendous
variety of marine life in the ocean, also gets very
excited, and runs into the water, disappearing.
The Chemist pulls out her notebook, and writes
"The Physicist and the Marine Biologist are
soluble in water"
• Far out to sea, the wind disturbs the calm
surface of the water. A ripple forms. As
the wind continues to blow, the ripple
grows into a powerful wave that can
travel a great distance. Near the beach,
surfers wait eagerly. They quickly paddle
into deeper water to catch the monstrous
wave. Surfers enjoy the power of nature
as they ride the wave to shore.
What are waves?
• Waves crashing on a beach
show the tremendous
energy waves can carry
• A wave is any disturbance
that transmits energy
through matter or empty
space.
Waves and Energy
• In science, energy is defined as the
ability to do work.
• To understand waves, think about a boat
out on the ocean. If a wave disturbs the
surface of the water, it will cause
anything floating on the water to be
disturbed too.
• The energy carried by a wave can lift
even a large ship as it passes.
What Carries Waves?
• Most waves require something to
travel through.
• Water waves travel along the
surface of the water and sound
waves travel through air.
• The material through which a wave
travels is called a medium.
What Carries Waves?, Continued
• Sound waves, water waves and
seismic waves all need a medium
through which to travel.
• Waves that require a medium
through which to travel are called
mechanical waves.
• Gases (air), liquids (water) and
solids (ropes) all act as mediums.
What Carries Waves?, Continued
• Not all waves require a medium to carry
them along.
• For example, light from the sun can
travel through empty space.
• Visible light waves, microwaves, radio
waves, and X rays are examples of
waves that can transfer energy without
going through a medium.
• These waves are called electromagnetic
waves.
What Causes Waves?
• Waves are created when a source
of energy causes a medium to
vibrate.
• A vibration is a repeated back-andforth or up-and-down motion.
• This motion is the source of the
wave.
What Causes Waves? Continued
• A moving object has energy.
• The moving object can transfer energy
to a nearby medium, creating a wave.
• For example, as the propellers of a boat
turn, they disturb the surface of the
water. The boat’s propellers transfer
energy to the water. The propellers
produce a wave that travels through
the water. As the boat moves through
the water, it also causes waves.
Types of Waves
• Waves are classified according to
how they move.
• The three types of waves are:
– transverse waves
– longitudinal waves
– surface waves
Transverse Waves
• When you make a wave on a rope, the
wave moves from one end of the rope to
the other.
• The rope itself moves up and down or
from side to side.
• When the vibration of a wave is
perpendicular to the direction in which
the wave is traveling, the wave is called
a transverse wave.
Transverse Wave
Transverse Waves
• All electromagnetic waves are considered
transverse waves.
Transverse Waves, Continued
• When you move a rope up and down,
some parts of the rope are very high
while some are very low.
• The highest parts of the wave are
called crests.
• The lowest parts of the wave are called
troughs.
Longitudinal Waves
• If you stretch out a spring toy and push
and pull one end, you can produce a
longitudinal wave.
• Longitudinal waves move the particles
back and forth (or parallel) along the
path that the waves move.
• The coils in the spring move back and
forth in the same direction as the wave
travels.
Longitudinal Waves, Continued
• In some parts of a spring, the coils are
close together and in other parts of the
spring the coils are more spread out.
• The parts where the coils are close
together are called compressions.
• The parts where the coils are spread
out are called rarefactions.
Surface Waves
• Surface waves are combinations of
transverse and longitudinal waves.
• Surface waves look like transverse
waves, but the particles of the medium
move in circles rather than up and down.
Surface Waves
• An object in open water will bob up and down as
the energy moves through, but the object will
not move forward.
Amplitude
• Some waves are very high, while others
are barely noticeable.
• The distance the water rises depends
on the amplitude of the wave that
passes through it.
• Amplitude is the maximum distance the
medium carrying the wave moves away
from its rest position.
Amplitude, Continued
• A wave with a large amplitude carries
more energy than a wave with a small
amplitude does.
Wavelength
• A wavelength is the distance between
any point on a wave to an identical point
on the next wave.
• A wave with a shorter wavelength carries
more energy than a wave with a longer
wavelength does.
Frequency
• Frequency is the number of complete
waves that pass a given point in a
certain amount of time.
• Frequency is usually expressed in
hertz (Hz)
• A wave that occurs every second has a
frequency of 1 Hz
• If two waves pass every second, then
the frequency of the wave is ?