Transcript Midway High School Science TAKS Review

Objective 5 – Motion
Forces and Energy (IPC 5)
IPC (5) (A) – Demonstrate wave types and
their characteristics
We encounter waves everyday.
When we hear the word “wave”
we tend to think of surfer dudes.
However, we don’t need to be near
water to experience waves
One common type of wave is
longitudinal, or compressional wave. In
a longitudinal wave, the particles of the
wave move parallel to the direction of
the wave. Sound is a longitudinal wave.
For a transverse wave, the particles
move perpendicular to the direction of
wave. Your favorite radio station
transmits transverse waves.
Two properties of waves are
wavelength and frequency. For
a longitudinal wave, a
wavelength is the distance
between successive
compression.
For a transverse wave, a wavelength is
the distance between two successive
crests (or troughs). Like all distances,
wavelength is measured in meters.
The frequency of a wave is the number
of waves that pass a point in space in a
given time period. So if 5 waves pass a
point in 1 s, the frequency of the wave
is 5 waves per second or 5 Hertz (Hz).
The product of the frequency and
wavelength is the speed of the wave.
v  f
Where v is the speed, f is the
frequency and λ (lambda) is
the wavelength. The speed is
measured in m/s.
Heerzwun: A sound wave has a
frequency of 256 Hz and wavelength of
1.3 m. What is the speed of the wave?
UTri: Two water waves strike the edge of a
dock every second (What does this
statement describe?). The speed of the
wave is 6 m/s. What is the wavelength?
IPC (5) (B) – Students will
demonstrate wave interactions
including interference,
polarization, reflection, refraction,
and resonance.
Waves interact with matter and with
themselves. They are very social.
One form of interaction is interference.
Interference occurs when two or more
waves occupy the same point in a
medium at the same time.
Interference of waves may be constructive
or destructive. When constructive
interference occurs, the amplitude of the
combined waves increases (i.e. sound gets
louder or light becomes brighter).
When destructive interference occurs, the
amplitude of the combined waves decreases
(so what happens to the volume of sound
and the intensity of light?)
Polarized waves are transverse waves that
are in the same plane. Notice, the vertical
wave may pass through the vertical
analyzer and the horizontal wave may pass
through the horizontal analyzer.
What happens when the
vertical wave is incident upon
the horizontal analyzer?
Reflection of waves enables us to
see the world around us. An
important property of a wave is
called the Law of Reflection.
The Law of Reflection states that for
any reflected wave, the angle of
incidence (the angle at which the wave
arrives, measured from the normal) is
equal to the angle of reflection (the
angle at which it leaves, also measured
from the normal).
Most of the reflection of light we
see is scattered (or diffuse). The
light is reflected from an object in
every direction. Some of the light
enters our eyes enabling us to see
that object.
Light is reflected from a
mirror or still body of water is
regular reflection. All of the
waves incident on the surface
that are parallel to each other
are also reflected parallel to
each other.
This type of reflection enables us to see
images in the surfaces.
If you view an object on the bottom
a swimming pool, the object
appears to be closer to the surface
than it actually is. This
phenomenon is described as
refraction.
Refraction is the bending of light as it
passes from one optical medium to
another, like air to water or glass to air.
How does refraction cause a straw in a
glass of water to appear to be split into
two sections?
Is it possible for a operatic soprano
to shatter a glass by singing a very
high pitch?
Actually, it is. This is an example of
resonance – two objects vibrating at the
same natural frequency. Almost all
objects have a natural frequency at
which they vibrate (glasses, loose
wheels on grocery carts, stadium
bleachers, bridges, etc.).
If one object vibrates at the same frequency
of a second object, this resonance increases
the amplitude of the vibration.
Describe the resonance in each case
 A child “pumps” his legs while swinging on a swingset
 A crowd rhythmically stomps and sways causing
stadium bleachers to collapse
 One person “rockets” another on a trampoline
(causing the second person to break her arm, thereby
suing the first person)