Traveling Waves

Traveling Waves


Hi. It’s Mr. Andersen. And this is AP Physics
essentials video 114. It is on traveling waves. Traveling waves are waves that move from one
point to another. They do not just keep bouncing back and forth. And Jeff Rowley was able to
ride this monster wave. And he was able to actually paddle into it. But when you watch
surfers like this, you will see them surfing waves that seem big, but the weather lots
of times is really nice. And so the reason why is that these waves came from somewhere
else. And so what increases the size of the wave? Well waves are created by wind blowing
over the surface of the ocean. So if you have a fast wind blowing over the surface of the
ocean then you are going to have bigger waves. We also could have the period of time over
which that wind is actually blowing. And then we have what is called fetch. Fetch is the
area over which the wind is blowing. So if you want to get a monster wave you have to
have high speed for a long period of time over a very large area. That is going to create
these traveling waves that move somewhere else. And so waves can be traveling or standing
waves. Traveling waves just like the name implies move from one area to another. But
standing waves appear to quote, unquote, stand still. It does not look like they are moving
at all. Now they actually are and what is happening is the traveling waves are bouncing
back and forth and due to interference they are creating these stand still or standing
waves. You should understand how we could get one dimensional interference between traveling
waves. And also two-dimensional traveling wave interference. You get what is called
a circular wave front. And then you can get these interference patterns. And so let’s
look at a traveling wave. This is a phet simulation. We are creating some waves. And this magical
simulation, the waves simply go out the door and the go on forever. And so the traveling
waves are created on the left and then they just keep going and going. But what happens
if we have a fixed point on the other side. When the wave gets to the other end, it is
actually reflected back. And it is inverted. No you can see it moving to the left. And
then boom, it is going to bounce back to the right. And so these traveling waves are going
back and forth and back and forth. And as they do that they create these standing waves
that appear to stand still. You will have these little nodes and antinodes, but they
are made up of traveling waves interfering with each other, bouncing back and forth.
An example of that is right here. We have these blue waves moving to the right. We have
these red waves moving back and forth. And then we have the summation of the two. We
have interference, which is creating this big wave, areas where it is not moving much
and areas where it is moving quite a bit. And so the reason why is due to constructive
and destructive interference. If we have two waves that are stacked right on top of each
other you will get these monster waves constructively built. And then if they are out of phase with
one another, what you will get is destructive interference, where they are actually canceling
each other out. Now it is not as regular as that. As waves interact what you will get
are these irregular patterns where we are having constructive and destructive interference.
These are actually beats that would be produced by noises or pitches that are a little bit,
slightly out of frequency. Now let’s go to two-dimensions. So if we are looking at
two-dimensions, in the simulation what I have got is water being dropped which is creating
these wave fronts that move out from the dropped water. And we are measuring it in middle.
But what happens if we have two drips of water that are coming down? Now we have two wave
fronts and as those wave fronts interact what we get is interference. You can see some areas
where they are canceling each other out. We have these grey areas where there is not much
waves. And then we have these darker areas, so let me pause this right here. So what we
had is if we are just measuring it along this length, you have big waves right at the beginning.
Large waves. And then it is kind of cancelled out. We do not have as big of wave in here.
And then those waves return on that side. And example of it if we look at it in a two-dimensional
kind of a simulation, if we are making waves that are the exact same frequency you will
get these huge areas where the waves simply cancel each other out. It is called an interference
pattern. And then we will have that constructive interference where we get these monstrous
waves in the middle. And so did you learn to analyze or evaluate interactions at one-dimension,
at two-dimensions as waves, traveling waves interact with each other? I hope so. And I
hope that was helpful.

23 thoughts on “Traveling Waves”

Leave a Reply

Your email address will not be published. Required fields are marked *