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
propagation is perpendicular to the direction of wave
-In a longitudinal wave the particle
displacement
is parallel to the direction of wave propagation.
-In a compressional wave the particle
displacement
similar to longitudinal.
occurs in compressions. Very
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 -
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. If the optical density of
Index of Refraction, Glass
same normal. - 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
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.