slides
jackblackVibrations and Waves
- Oar in Water
- Wings of a Bee
- Electrons in an Light Bulb
- Water Waves
- Sound Waves
- Light Waves
“Wiggles in Time”
“Wiggles in Time and Space”
In the above diagram the white line represents the position of the medium when no wave is present. This medium could be imagined as a rope fixed at one end a few feet above the ground and held by you at the other end.
The yellow line represents the position of the medium as a wave travels through it. We simply say that the yellow line is the wave. If we consider the rope mentioned before, this wave could be created by vertically shaking the end of the rope.
Often, when several waves are traveling along a medium as shown above, the continuous group of waves is called a wave train.
The section of the wave that rises above the undisturbed position is called the crest. That section which lies below the undisturbed position is called the trough. These sections are labeled in the following diagram:
amplitude
To sum up amplitude, we would say:
-It is the displacement of the medium from its normal position.
Usually this simply means the maximum positive displacement.
-Often, especially in discussions about interference, amplitude means the displacement of the medium from its normal position at certain points, and this displacement can be positive or negative.
-Think of the amplitude as the Energy of the Wave.
Wavelength
The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train. This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting point. This is shown in the following diagram:
Actually, the a wavelength exists between any point on a wave and the corresponding point on the next wave in the wave train. A few of such distances are shown below:
Frequency
Frequency is often not termed as a part of a wave, but it makes sense to introduce its meaning in this section.
Frequency refers to how many waves are made per time interval. This is usually described as how many waves are made per second, or as cycles per second.
If ten waves are made per second, then the frequency is said to be ten cycles per second, written as 10 cps.
Usually, we use the unit Hertz to state frequency. A frequency of 10 cps is noted as a frequency of 10 Hertz. So, one cycle per second is one Hertz, as in:
1 cps = 1 Hertz
The unit Hertz is abbreviated this way:
1 Hertz = 1 Hz
Wave in time and space
Longitudinal Waves
In a longitudinal wave the particle displacement is parallel to the direction of wave propagation. The animation below shows a one-dimensional longitudinal plane wave propagating down a tube. The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region (ie, it is a pressure wave), which moves from left to right.
Transverse Waves
In a transverse wave the particle displacement is perpendicular to the direction of wave propagation. The animation below shows a one-dimensional transverse plane wave propagating from left to right. The particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by. Pick a single particle and watch its motion.
Water Waves
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. The radius of the circles decreases as the depth into the water increases. The movie below shows a water wave traveling from left to right in a region where the depth of the water is greater than the wavelength of the waves. I have identified two particles in blue to show that each particle indeed travels in a clockwise circle as the wave passes.
http://www.teachersdomain.org/ext/ess05_int_wavemotion/index.html
http://www.kettering.edu/~drussell/demos.html
Raleigh wave in solids (like an earthquake)
Notice that on the surface, the particles are rotating in an ellipse counterclockwise but down a little, they are traveling in an ellipse in the opposite direction (clockwise)