WAVES – Benchmarks & Standards
3.1
THE STUDENT WILL INVESTIGATE WAVELENGTH, FREQUENCY,
AMPLITUDE, AND VELOCITY AS PROPERTIES OF WAVES. [P8C1,
P8C2]
3.2
THE STUDENT WILL DESCRIBE HOW WAVELIKE DISTURBANCES
SPREAD UNIFORMLY AWAY FROM THE SOURCE. [P8C2]
6.3
THE STUDENT WILL EXPLAIN THAT ATOMS AND MOLECULES ARE
IN CONSTANT MOTION. [P8A1]
7.3
THE STUDENT WILL INVESTIGATE ENERGY AS A PROPERTY
ASSOCIATED WITH MATTER. [P8C4]
P8A1
Students know particles are arranged differently in solids,
liquids, and gases of the same substance. E/S
Solid
Liquid
Gas
Plasma
Example
H20 = Ice
H20 = Water
H20 = Steam
H20 = Electrically
Charged Gas
Common
Common on earth
Common on earth
Common on earth
Common in universe
Temperature
Cold
T < 0 °C
Warm
0 °C < T < 100°C
Hot
T > 100 °C
Super Heated
T > 100,000 °C
Energy
Low energy
High Energy
Very High Energy
Extreme Energy
Shape
Definite shape
Indefinite shape,
takes shape of
container
Indefinite shape, fills
entire container
Indefinite shape
Volume
Definite volume
Definite volume
Indefinite volume
Indefinite volume
Density
Most densemolecules tightly
packed
Medium densedepends on liquid
being tested
Least densemolecules far apart
, depends on gas
Ionized, charged
particles, far apart
Vibration of
molecules
Vibrate in a fixed
position, structure
Vibrate and slide
freely across each
other
Vibrate and move
freely, large spacing
Ions and electrons
move & vibrate
freely
Elasticity
Most elastic- bounce
back after being
disturbed
Not very elastic- do
not bounce back
after being
disturbed
Low elasticitybounce against each
other, but not back
to original
Low elasticity
Molecular
Arrangement
Notes Page 3
What do all of these states of matter
have in common?
• Matter- the substance that objects
are made of; anything that has
mass and takes up space
• Matter is made up of particles which
are in continual random motion.
– Absolute zero?
• If it were possible to attain a temperature
absolute zero for a material then all the
vibrations/random motions will stop.
Presently, it is not possible to reach
absolute zero
• Solids, liquids and
gases are all
examples of states
of matter that
waves travel
through.
Waves Vocabulary
• Vibration- a repeated
(periodic) back and forth or up
and down motion
• Energy- the ability to do work
• Wave- a rhythmic disturbance
that travels from one place to
another transporting energy
only, NOT matter
– Waves get their energy from the
source of vibration or disturbance.
– Waves transfer energy from one
place to another.
– The amount of energy a wave
transfers decreases as the wave
moves away from its original
source.
• Mechanical Wave- a wave that
requires a medium to travel
through
– Ex. Sound!
– Most waves need a material,
called a medium to travel through.
The particles of the medium do
not get carried along with the
wave.
• Electromagnetic Wave- a wave
that does not require a
medium to travel through
– Ex. Light!
• Vacuum- a space that contains
nothing—complete emptiness
– Most of the universe is filled with
vacuum
The “Ripple Effect”
Page 4
• Waves spread outward in all
directions from the source
• Sketch diagram ->
Light vs. Sound
Longitudinal Waves
• Longitudinal wave: Mechanical waves in which the particles of the medium moves
parallel (forward and backward) to the direction the energy of the wave is traveling
• Compression: particles of medium are close together
• Rarefaction: particles of medium are spread out
Transverse Waves
• Transverse wave: waves that move the particles of the medium perpendicular
(at right angles) to the direction in which the energy of the wave is traveling
• Crest: highest part of transverse wave
• Trough: lowest part of transverse wave
• Surface Wave – Combination of
transverse and longitudinal waves
• Surface waves occur at the
boundary between two mediums
of different densities
• Example: When a wave passes
through water, the water moves up
and down, as well as back and
forth. This movement causes the
water particles to move in circles.
• Unlike the coil of a slinky, the water
does not compress.
Surface Wavespage 4
Page 6- Amplitude (A) – amount of energy in a wave
Longitudinal Wave
•
The measure of how compressed
or rarefied the medium becomes
– Tighter compression =
greater energy
– Looser compression = lower
energy
Loose Compression
= Low Energy
Tight Compression
= High Energy
Normal-to-Crest
Normal-to-Trough
Transverse Wave
•
•
The distance a transverse wave rises from the resting
position, called the amplitude, depends on the energy
of the wave that passes through it.
Measured Normal-to-crest or Normal-to-trough; The
height of a wave from the normal
– Greater amplitude = lots of energy
– Lower energy = lower amplitude
Wavelength (λ) – length of the wave
Longitudinal Wave
The distance from:
• Compression-to-Compression
• Rarefaction-to-Rarefaction
Wavelength
Transverse Wave
The distance from:
• Crest-to-crest
• Normal-to-normal
• Trough-to-trough
Wavelength
Wavelength
Wavelength
Wavelength
Frequency – The number of complete waves that pass a
given point in a certain amount of time
• Frequency is also the number of vibrations per second.
High Frequency
Low Frequency
Hertz (Hz) - Basic SI Unit for frequency; the
number of complete cycles per second
• Frequency is measured in Hertz.
Named after Heinrich Hertz, a
German physicist who studied
electromagnetic waves.
– 1 wave per second has a
frequency of 1 Hz.
– 2 waves per second has a
frequency of 2 Hz.
Period
• Period- The time it takes a wave
to complete a full wave cycle
– In a time of one period, the wave
has moved a distance of one
wavelength
– Inverse of frequency
• Ex. Frequency = 5 Hz
• Period = 1/5 s
Speed/Velocity• Speed- the distance an object travels in one
unit of time
– ex. 25 miles per hour
• Velocity- speed with a direction
– ex. 25 mph, North
The Wave Equation- formula for relating
speed/velocity (v), wavelength (λ), and
frequency (f)
• Speed = Wavelength × Frequency
V=λ×f
• Wavelength = Speed
Frequency
• Frequency = Speed
Wavelength
• Mathematical Equation in Words:
– As wavelength increases, frequency decreases.
– As wavelength decreases, frequency increases.
• Elasticity- the tendency of
a material to maintain its
shape and not deform
whenever a force or stress
is applied to it
• More elastic = the faster
the wave travels
• Waves travel faster
through solids than they
do liquids, and faster in
liquids than in gases
• vsolids > vliquids > vgases
• Which material is more elastic?
– Steel vs. Rubber?
– Steel!!
• Steel = maintains shape = high elasticity
• Rubber = deforms easily = low elasticity
• The molecules of elastic materials are very
attracted to each other, so the particles
return to their resting position quickly, and
are ready to move again more quickly. So,
they vibrate at higher speeds!
• Density describes the mass of a
substance per volume
• Density of a medium is the
second factor that affects the
speed of sound
• Usually, larger molecules have
more mass.
– Denser because molecules are
larger = Transmit sound slower
– Why? It takes more energy to
make large molecules vibrate than
it does to make smaller molecules
vibrate
• Sound is a vibration of kinetic
energy passed from molecule
to molecule.
– The closer the molecules are to
each other and the tighter their
bonds, the less time it takes for
them to pass the sound to each
other and the faster sound can
travel.
• Molecules close together =
travel fastest
– come into contact with one
another more frequently
• Molecules spread far apart =
travel slowest
– Do not come into contact with
one another very often
• Travel through solid medium faster than all other states of matter,
because molecules are closer together and can transfer energy
easier
•
•
It is easier for sound waves to go through solids
than through liquids because the molecules are
closer together and more tightly bonded in solids.
It is harder for sound to pass through gases than
through liquids, because gaseous molecules are
farther apart.
• But what if we are only comparing gases
(Helium vs. air)?
– Sound travels faster in a less dense material
than in a more dense material of the same
state of matter
– Sound waves travel 3x faster in Helium than in
air—causes the high pitch voice!
– Why? Helium molecules have less mass than
air molecules!
• Hotter material = faster
molecular motion = faster
speed of sound
• Colder material = slower
molecular motion =
slower speed of sound
• Therefore, sound travels
faster in warm air than in
cool air