This is the first lecture on waves, and these are the topics we're going to be talking about.
This is the definition of a wave. A wave is a disturbance that carries energy through a medium
without carrying matter along with it. All waves have common physical properties we can describe
and calculate. The particles in the wave exhibit simple harmonic motion. So I'm going to play
these two animations and have you observe what's happening as the wave moves through the matter.
Notice first of all that these two animations show you every particle in the medium that the
wave is moving through. So you can see that even though the wave is moving through the medium,
in either animation that you look at the particles themselves are being pushed back and forth by the
wave, but they're not really being carried along with it. They're just oscillating back and forth
in simple harmonic motion. So this is what I mean when I say that a wave does not carry matter along
with it. Any particle that you look at within the matter is moving back and forth, but it's staying
within that same region. It's just oscillating back and forth as the wave moves through it. So
that part of the definition is really fundamental: to be a true physical wave, it cannot carry that
physical matter that it's moving through along with it as it moves, and every single particle
inside of that wave exists in simple harmonic motion. It's oscillating back and forth around a
point of equilibrium. So we're going to talk about this more as we go through the lecture. There are
two wave shapes we can talk about: transverse and longitudinal waves. A transverse wave is a wave
that oscillates matter in a perpendicular direction to the waves in motion, and the
longitudinal wave is a wave that oscillates matter in a parallel direction to the waves motion. So
I'm gonna play these animations and show you what I mean by that. You can see in the transverse wave
the wave is moving from left to right, but if you observe what any one particle in the wave
is doing, that one particle is only moving up and down. So the oscillation of the matter is
perpendicular to the direction of the wave. The wave is moving from left to right and the matter
is moving up and down, so that's the definition of a transverse wave. That's what makes something a
transverse wave. In the longitudinal wave you can see that the wave is moving from left to right and
the particles in the wave are also oscillating back and forth from right to left to right
to left, so they're oscillating in a parallel direction to the direction of the wave. So that's
what makes the wave on the right a longitudinal wave. For most tests you're going to need to
be able to list some examples of both types of waves. I'm going to go through some examples of
each right now. One example of a transverse wave is a string on a musical instrument. You'll notice
that transverse waves are being created when this person plucks the guitar strings. So this occurs
with all stringed instruments. Moving a slinky up and down, we can actually use slinkies for
both types of waves but here this is an example of a transverse wave. Doing the wave at a sports
game is also an example of a transverse wave because the wave is moving along the stadium,
but the people themselves are moving up and down in a perpendicular direction to the wave's motion.
I'm going to add here that electromagnetic waves are also transverse. You don't know
what those are yet so we'll talk about that more later. For now you'll just have to remember that
that's another example of a transverse wave. A common example of a longitudinal wave is sound,
because sound is just another example of a wave in matter. Normally we hear it in air
particles specifically. You can see in this animation I'm showing all the individual air
particles that are bouncing up and down or left and right as the sound wave moves through them,
so you can clearly see the wave radiating outward from the speaker in the center,
but if you watch any one particle you'll see that that one particle is bouncing forward and back. It
isn't being carried along by the wave, and if you look at the oscillation of any one particle you'll
notice that that oscillation of that particle is parallel to the direction of the wave's motion at
that one point. So I've highlighted the particles on the left and right of the speaker, but even if
you look in the up or down direction you'll see that where the wave is moving up the particles are
moving up and down and where the wave is moving down the particles are also moving up and down.
Slinkies are also useful for creating longitudinal waves because you can push them forward and back
like this and create this wave pattern. So this is another example of a longitudinal wave. Another
difference to note is the difference between mechanical waves and electromagnetic waves. So
a mechanical wave is a wave that requires a medium to move through, some substance to move through.
It oscillates matter and it can be transverse or longitudinal. So just as an example, an ocean
wave requires the ocean in order to exist in the first place. If there wasn't water we wouldn't
really be able to describe ocean waves at all. So mechanical waves are any wave like that that needs
some medium to move through in order to exist. If there's no medium, the wave itself does not
exist. Electromagnetic waves are a special type of wave. It's the only type that moves through
empty space. Electromagnetic waves are created as a result of the vibrations between electric
fields and magnetic fields. Ell electromagnetic waves are photons, which are particles of light,
and all move at the exact same speed: the speed of light, which we call lowercase c in physics,
and that speed is 3.00 x10^8 m/s. The only way they're different from each other is in
their wavelength and frequency, but their velocity stays the same at that speed of
light. So those are some basic definitions of waves that you will need for this unit.