Hi. It's Paul Andersen and this is disciplinary core idea PS4A which is on
wave properties. Waves are incredibly important and they're relatively simply to understand.
But most students don't get it. And so the first thing you should understand is that
there's really only two ways that we can move energy from place to place. If I want to move
energy from where I'm at to somewhere else, I could do it using particles. I could thrown
something around the room. Or I could used waves. So I could use my voice. Or I could
use light. Or I could also use electric currents to move energy from place to place. And so
they're incredibly important and they have relatively few properties. And so what is
a wave? It's simply a disturbance. And if we look at a typical wave they're all going
to have a wavelength. And that's going to be just the distance of a wave. How big a
wave is. We could measure it here. Or we could measure it from crest to crest, or trough
to trough. But it's how long that wave is. Also they're going to have a frequency. Frequency
is the number of waves you're going to have in a given period of time. So if you were
to listen to a real low frequency sound, that's going to be a few number of waves in a given
period of time. But if it's a high frequency sound it's a lot of waves in a given period
of thine. And these two things are related to the medium that it is moving through. And
that's an important characteristic of waves. Waves are moving through a medium. So for
example, sound is moving from my voice to the microphone through air. But the medium
doesn't move. The air doesn't move. Well how could I change the medium that I'm speaking
through and change the frequency of those waves? Have you ever inhaled helium? What
does that do to your voice? Well it changes the medium of the air inside your vocal cords
and you get a high pitched frequency. Likewise if you had a real low density gas that you
were to breath in you would have a low frequency or a low noise. What's another property of
waves is going to be their amplitude. Or it's the size of the wave. And so the volume of
my voice is related to the amplitude of those waves. Waves can be used to store information.
So we can put information, we can digitize it for example, and we can send it as a wave
from location to location. So not only are you hearing my sounds from the speakers of
your computer, but you're accessing this through the internet. And so you're receiving that
as a wave. So they're incredibly important. Let's talk about a few concepts, starting
with sound. So what is sound? Sound is simply an oscillation or disturbance in air that's
transmitted through the air. And so if we ring a bell right here, the wave is moving
out. It's kind of a compressional wave that moves out from where ever the sound is created
to where it's received. But the air doesn't move from location to location. Likewise it's
going to vibrate your eardrum in your ear. And you're going to start to perceive that
as sound. What if we take away the air? Then you can't hear anything. And so in space you're
not going to have sound because there's no medium. What's another characteristic? Resonance
is important as well. And so first we have to take about interference. Let's say we have
two waves that are right on top of each other. And these waves are in sync. So when the crest
of one is right next to the crest of another. And the troughs as well. So those are going
to interfere with each other. And what you'll get is a bigger wave. A wave that's a combination
of those two. Likewise if we had two waves that are the same size, but they're out of
sync with one another, it would actually cancel each other out. And so you should know that
waves can interfere with one another. And what's a property then that we can have from
that? Well if you've every pushed somebody on a swing, you realize that you have to push
them at the right point if you want them to get higher and higher and higher. So by pushing
them at the same point what you're really doing is adding, you're interfering with that
wave. And so let's say that we had a string for example. If we vibrate a string, the wave
is going to go down one side and it's going to come back the other. Down onside and comeback
the other. And what eventually you get is as those waves are moving back and forth,
they're interfering with each other. So you'll have some points where you're building up
the wave. And sometimes where you're canceling it out. And so we call that resonance. And
you've experienced resonance if you've ever sang in the shower. You'll notice that if
you hit one pitch in the shower it's going to sound really really good. And that's because
the waves bouncing around are interfering with each other. And they're building themselves
up. And all instruments are built on this idea of resonance. What are some other characteristics
of waves? Waves aren't going to run into objects if the objects are too small. So if we have
an object that's really, really small, a wave will simply miss it. And that's really important
when we're talking about the waves of light. If we have really small objects like an atom,
light can't even hit it. And it's not going to be a, it's not going to be reflected. Or
it's not going to bounce off of that. Likewise when we change the medium we can change the
speed of the wave. And so what's an example of that? Right here we have some glass. So
we have a lens right here. And as the light is moving towards it, it's bending as it moves
from one medium to another. And so as waves move from medium to medium they can be transmitted
through it. They can reflect off of it. But weirdly they can also bend in response to
that medium as well. And so diffraction, excuse me, refraction that we see, like here is a
little bit of water on a glass and it's refracting the light coming from the Golden Gate Bridge,
so it's actually bending that light and we're getting an image that's upside down. So how
do you teach all of this through the school? You want to start in the lower elementary
grades by talking about simple waves. And water waves are a great place to start. Fill
up a little pan of water and start generating some waves. And what you'll notice is that
the waves will move from the area where the disturbance is. But the water is not going
to move. What would be a good way to demo this? We could put some color in it, food
coloring. Generate some waves. And we'll notice that the food coloring takes much longer to
move out than the wave does. Also you should get this understanding that sound can vibrate
matter. And so an example would be right now the sound waves that I'm producing are vibrating
the microphone that's picking up those sounds. And likewise, matter can vibrate and it can
produce sounds. And so this big base drum, if you hit it, it's vibrating back and forth.
And that's generating that sound. Likewise if we were to generate enough sound we would
start to vibrate that bass drum as well. As you move into the upper elementary grades
you want to talk about waves interfering with one another. And so let's say we have this
wave and this wave and they're going to move towards each other. What will happen right
when they get to the middle is that they'll build a larger wave when they hit. And so
they're going to build on each other. They're going to increase the amplitude of that wave.
Likewise if we have two waves that are opposite, one wave on this side, one wave on the other
side, what happens to them is when they hit each other they're actually going to interfere
in a negative amount. Likewise that really explains a few things. Number one it explains
resonance. Why we can get waves building each other up. But also you have to understand
that as those waves move through each other they're going to merge unaffected. In other
words waves are going to interfere, but overall they're not going to cancel each other out.
They just keep moving. And so what's an example of that? Imagine if you had a bunch of people
talking in a room. They're all generating sound waves. But they're not like destroying
each other's sounds. All those sounds are moving through each other throughout the room.
Another think you want to talk about in elementary grades is the idea that earthquakes are simply
waves in the earth. And we call those seismic waves. And so what's happening is we have
some disturbance that's being transmitted through the earth. As we move into middle
school we want to start talking about the parts of a wave. You should identify the wavelength
and the frequency. Remember the frequency is going to be the number of waves we have
in a given period of time. And then also the amplitude of the wave. And remember that they
require something to move through. So sounds, it moves through a material to generate a
wave or a water wave. The only exception to this is radiation, like light. And we'll talk
about that in a future video. Also you want to talk about the earth and the structure
of the earth. And how do we know what's on the inside of the earth? Because we've tried
to drill into the earth. We can just barely get into the crust a little bit. So how do
we know that there's a solid core on the inside? It's as these earthquakes are moving through
the earth we can see how they bend. How they move. How fast they move. And we can figure
out what the inside of the earth looks like. As we move into high school we want to start
to quantify this a little bit. And students should understand that wavelength and frequency
are inversely proportional. What does that mean? As we increase the frequency, increase
the number of waves we have in a given period of time, what's that going to do to the wavelength?
It's going to make the wavelength get smaller. Likewise as we decrease the frequency we're
going to have wavelengths that get much much larger. Also we want to talk about refraction,
reflection and transmission. And so when one wave bounces off a medium, so right here we
have air and then we have glass, so we have a little prism right here. Some of that light
is going to be reflected or bounced off of that. Some of it is going to be bent or refracted.
And that only occurs when we move from one medium to another. But also some of that light
here is going to be transmitted through. And what are some applications of waves in our
lives that make them important? Well the first one would be the idea of information. So information
like you're seeing my image right now on an LCD projector or maybe you're seeing it on
your computer screen, those are just pixelated information. But that information is being
transmitted to your screen or to the projector as a wave. And a lot of that information is
stored inside the computer itself as waves. Likewise if we're talking about resonance,
why is that important? All instruments are really working on this principal of resonance.
And so we get resonance in the strings or a string instrument. But we also get resonance
in a horn for example and a flute is resonance of the air waves within that flute or within
that horn. And so waves are incredibly important. They have a few simple properties. But I hope
that was helpful.