Transcript Slide 1

Yeah
Science!
A rock tossed into the water will
create a circular disturbance
which travels outward in all
directions…
AMPLITUDE-Distance from the midpoint to the crest (also equal to
the distance from the midpoint to the trough)
CREST- The Highest Point of a Wave
TROUGH-The Lowest Point of a Wave
MIDPOINT-Halfway between the Crest & the Trough.
WAVELENGTH-The distance from one Crest to the next Crest.
TRANSVERSE-In a transverse wave the particle
displacement is perpendicular to the direction of wave
propagation
LONGITUDINAL-In a longitudinal wave the particle
displacement is parallel to the direction of wave
propagation.
COMPRESSIONAL-In a compressional wave the
particle displacement occurs in compressions. Very
similar to longitudinal.
What about Waves in Water? Which type are they?
Transverse waves are always characterized by particle
motion being perpendicular to wave motion.
Water waves are an example of waves that
involve a combination of both longitudinal and
transverse motions. As a wave travels through
the waver, the particles travel in clockwise
circles.
What do we mean by medium?
A material (solid, liquid, or gas) through which a
wave travels.
Why does this pencil appear broken or bent?
Light travels at a different speed in water than
it does in air.
300,000 km per second in empty space
225,000 km per second in tap water
• So this bending is caused by
REFRACTION.
• Refraction is the bending of light at an
interface between two materials.
The light doesn’t slow down, it just get
“delayed” as the energy is absorbed and
passed on from one atom of the medium
to the next.
The “Disappearing Glass”
In this demonstration, I will have a small
(200 or 250 ml) beaker inside a larger
(1000 or 2000 ml) beaker. The small
beaker is easy to see. Then I will pour
Wesson Vegetable Oil into the small
beaker, overflowing it and continuing to
pour as it fills the larger beaker. As the
larger beaker fills, the smaller beaker will
seem to disappear, except for any
markings it has. At this point, I will again
ask for explanations. This time, the
reason is not readily apparent. Through
guided discussion, I will lead the class to
the conclusion that the cooking oil and
the glass have the same index of
refraction (about 1.5), and thus bend light
rays the same. This makes them
indistinguishable from each other in the
large beaker, and thus makes the beaker
seem to “disappear”.
Index of Refraction, Liquids - Hold a circular protractor in a vertical position and
submerge half of it in a large beaker of liquid. Aim the laser do the beam just grazes
the front surface of the protractor and passes through its center. Measure the angles
of incidence and refraction. Calculate the index of refraction of the liquid using the
relationship n=sin i/sin r. Repeat for different angles of incidence and for different
liquids. Water, alcohol, and glycerin are suitable for this exercise.
Index of Refraction, Liquid with Varying Optical Density - If the optical density of
a liquid or a gas varies, a light beam will bend gradually as it is transmitted through
the fluid. This can be observed by partially filling a fish tank with clear water and
adding several lumps or cubes of sugar solution that is dense at the bottom and
gradually becomes less dense toward the surface.; Aim the laser beam horizontally
into the side of the tank and observe how the beam gradually bends as the index of
diffraction of the sugar solution increases.
Index of Refraction, Glass - When light travels from air to glass, there is a change
of speed and the beam will bend, or refract, at the interface when it enters the glass.
Measure the angle (i) between the incident laser beam and the normal to the glass
surface. Also measure the angle ( r) between the bent beam inside the glass and the
same normal.
Index of Refraction, Prism - When a laser beam is transmitted through a triangular
prism, the beam will be reflected twice and emerge along a path that deviates from its
original direction of propagation. By rotating the prism, the angle deviation can be
obtained is called the minimum angle of deviation for the particular prism. By
measuring the apex angle of the deviation, the index of refraction of the prism may be
calculated: Greater precision can be obtained by allowing the beam to cross a room
so that small changes in angle will be greatly exaggerated because of distance.
Angle of Reflection
= Angle of Incidence
Angles are measured
with
respect to the normal
line
(the perpendicular line).
If you clap your hands in a large, empty room, you may hear
the echo from the sound of the clap bouncing off the far wall
and returning to you. Pulsed ultrasound imaging technology is
similar to the clap and echo.
If you could accurately measure the time it took from your
handclap to the time you heard the returning echo, you could
calculate how far the sound has traveled, and by inference,
how far away the wall is from you.
distance = (time) x (speed of sound in air)
Depth of wave action is equal to
1 half wavelength.
So you wanna see real waves?
Follow the simple directions on
the next slide to create a wave
bottle.
Consider adding glitter or
particles of different densities.
Allow students to actually see
that waves are only ENERGY
moving through the medium.
There is no net change in the
position of the “floating”
particles.
Wave Bottle
Grade Levels: 6-8
Objectives
Students will observe water moving in waves.
Students will discuss why waves move in similar patterns. Students will realize that a wave
is ENERGY moving through a medium not PARTICLES moving through a medium (that
would be a current)
Materials
A 1 liter plastic bottle for each student.
Vegetable oil
Food coloring
Water
Paper
Pencils
Procedures
Give each student a plastic bottle.
Ask students to fill the bottle two-thirds full of water.
Direct students to add a few drops of food coloring to the water.
Ask students to fill the bottle to the top with oil, then screw on the top tightly.
Tell students to turn the bottle on its side and gently roll it around to make waves.
Instruct students to draw a few pictures of the waves they see.
Direct students to write down anything they notice about the movement of the waves.
Have a class discussion about why students think the waves move the way they do.
As an extension activity, discuss other factors that might effect waves such as the ocean
floor, sandbars, rocky coasts and, of course, the moon.
Need to reinforce concepts for ESOL, SPED, or
Remedial learners? Click the link below.
I don’t
get it!
Students form a straight line (shoulder to shoulder) and
connected themselves to their nearest neighbor by meter sticks.
A strip of masking tape divides the parking lot into two "media."
In one of the media (on one side of the tape), students walked at
a normal pace. In the other media (or on the other side of the
tape), students walked very slowly using baby steps. The group
of students walk forward in a straight line towards the diagonal
strip of masking tape; the students maintain a line as they
approach the masking tape. When an individual student reaches
the tape, that student abruptly changes the pace of her/his walk.
The group of students continues walking until all students in the
line have entered into the second medium. The diagram below
represents the line of students approaching the boundary
between the two medium (the masking tape). On the diagram, an
arrow is used to show the general direction of travel for the group
of students in both medium. Observe that the direction of the
students changes at the "boundary."
The Marching Soldiers Analogy
Students joined by
meter sticks
walking to the
right.
Direction of the line
of students has been
altered.