Hi. It’s Mr. Andersen. And this is AP Physics essentials video 100. It is on transverse
and longitudinal waves. And this is the Kola Superdeep Borehole. It is a covering over
the deepest hole that humans have ever dug. The Soviets did this in the 1970s. They got
around 40,000 feet below the surface of the earth. It got incredibly hot. They could not
keep drilling but it is really deep. If we were to look at the earth however that is
barely scratching the crust. And so you might think to yourself, how do we know what the
inside of the earth looks like if we have only been able to dig and little bit into
the crust. Well it is thanks to waves. Seismic waves, waves produced through earthquakes.
Some of those are transverse waves. Those are waves where the oscillation is perpendicular
to the motion of the wave. And those ones, like all waves, cannot make it through the
solid inner core but also cannot make it through this liquid outer core. But the longitudinal
waves where their oscillation is in the direction of the motion can still move their way through.
So we are looking at those waves on the other side of the earth to figure what the inside
of the earth looks like. And so waves are simply ways to transfer energy through disturbances
or through oscillations. And they come in two forms. We have longitudinal waves. That
is where the oscillation is in the same direction or parallel to the propagation or the movement
of the wave itself. We also have transverse waves. And transverse waves, the motion in
this case would be left to right, but the oscillation is going to be perpendicular to
that. And so all of these can be mechanical waves. Mechanical waves, like the seismic
waves in the earth require a medium. They require something to go through. And they
could be longitudinal or transverse. However electromagnetic waves, like the light that
you are receiving right now is only formed in transverse waves. It does not require a
medium for it to move through. It can move through a medium like right now it is moving
through the air inside your room. An interesting characteristic of transverse waves is they
can be polarized. And so we can use thin slits to only let certain transverse waves through.
And so energy can be moved from point A to point B in two ways. It could be a particle
that we simply fire a particle from A to B. And we could move B. But we could also use,
in this case, a medium and at point A we could make oscillations which would generate waves
if B is a piece of paper on that it would float and move away. So we are transferring
energy from one point to another but there is no particle that makes it there. Remember
that those waves can be either mechanical, so the waves we would find in an ocean or
the waves of sound are all mechanical waves. But we can also have electromagnetic waves.
And those electromagnetic waves can move through no medium. They can move through space where
there is nothing. And so if you were to really see an explosion in space, you would not hear
it because there is no medium for those mechanical sound waves to reach you. But you would definitely
be able to see it. And so the two types of waves are longitudinal. Longitudinal are waves
where the oscillation or the disturbance is in the direction that the wave is moving.
So you can see in this first animation that we have the wave moving from left to right
and we also have the oscillations moving from left to right. An example of this could be
a pressure wave. An example of that could be like the sound waves that you are hearing
right now. I am vibrating the air which is vibrating this microphone which is vibrating
your speaker which is vibrating the air near you and then you can hear that. But everything
is in the same direction. If we were to look at this simbucket simulation down below the
green particles, as they move back and forth is transferring energy from left to right.
That is represented by the dotted line right here. But you can see that the particles are
moving in the direction that the wave is actually moving it. And so that is a longitudinal wave.
What does a transverse wave look like? Well I always think of the T in transverse. It
tells me that it is going to be perpendicular to the motion. So if we were to do the same
kind of an animation, right here again, the propagation or the movement of the wave is
from left to right but you can see that the oscillation is up and down. An example of
this could be a rope wave. If you attach a rope to a wall and just simply oscillate it
or light could be an example of that. If we look at simbucket simulation down below, this
time we have a rope wave. It is going from left to right, but know where the oscillation
is. The oscillation is up and down. Another interesting thing is that the rope is not
moving, it is the energy that is moving from one spot to another. It is not like the air
moves, it is the energy moves through the air itself. And so one interesting thing about
transverse waves is that they can come in many different directions and since it is
perpendicular to the motion we can have a grid or a slit or some kind of a filter here
that will only let transverse waves that are going in one direction through. And so polarized
sunglasses work like that. This is an image where we have no polarizer on the bottom.
And so we are getting light in all directions. But then when we are using a polarizing lens
at the top then you can see the photographer on the inside because light is only coming
out through the car itself. And so did you learn to use visual representations of longitudinal
and transverse waves? Have you learned how to use a model to study them? And then in
AP Physics II, do you understand the importance or polarizing as a way to limit only a certain
direction of transverse waves moving through? I hope so. And I hope that was helpful.