Hi. It’s Mr. Andersen. And this is AP Physics
essentials video 103. It is on wave energy
which is directly related to wave amplitude.
If we were to look at waves in the ocean,
as the wind blows over the surface of the
ocean, you get these surface waves. You can
see there is less energy the farther we go
down. The water is kind of moving in this
circular path, but we are transferring energy
from point A to point B. How much energy is
dependent upon the amplitude of the wave.
And so the higher the crest and the lower
the trough the more energy there is. And we
are letting that go. And humans are looking
at that right now. They are installing these
wave energy generators. This one is off the
coast of Portugal. And this one will be off
the coast of Oregon. And what they will do
is as they move up and down they are running
a little turbine and it is generating some
electricity. And so waves transfer energy
through oscillations. Those oscillations can
be longitudinal in longitudinal waves. That
is where the oscillations are parallel to
the movement of the wave. Or they can be transverse,
where they are perpendicular. In both case
the maximum displacement, how big the wave
is is the amplitude. And since waves transfer
energy the amplitude is a direct measure of
the amount of energy. And a longitudinal wave,
we could measure that using the density changes,
within the compressions. In a transverse wave
it is easier. We just measure how high the
crest is, how low the trough. But again it
is directly related to the energy being transferred
through the wave. So let’s say we are looking
at sounds waves, for example, which are a
longitudinal wave, what would be the amplitude
of a sound wave? It is not going to be the
pitch. It is going to be the volume of the
wave itself. How big is that wave. So let’s
take a look at wave amplitude using a simbucket
simulation. So we have a rope wave here. You
can see the wave is moving from left to right.
But the oscillation is perpendicular. So this
is a transverse wave. But as I increase the
amplitude, what is happening? You can see
there is greater and greater oscillations.
What does that imply about the wave energy?
The higher the amplitude, and the lower below
equilibrium, the greater energy that we have.
How could you measure that? If we have a static
picture, you simply measure how high and how
low. That is the wave amplitude. Now let’s
say we are listening to a sound. It is hard
to see that. And so we can use the volume
to measure that. Let me play a note for a
second. This is “A”. I could have different
shapes and it sounds different. I could change
the frequency and the pitch will change. But
it is still carrying the same amount of energy
because the waves have the same height. How
could I change the amount of energy in a sound
wave? Well we could do that by simply changing
the volume. And so that is the amplitude.
So if I take that pitch and I lower the volume
or I raise the volume, then the amplitude
gets greater. And therefore the amount of
energy that that wave, in this case sound
wave, is actually transferring. And so did
you learn to explain or predict qualitatively
how the energy is related to the amplitude of a wave?
I hope so. And I hope that was
helpful.
