Hi. It's Paul Andersen and welcome to disciplinary core idea PS3A which is on
definitions of energy. We can look at a lightning strike and we know that there's energy there
somewhere. But a question that we've always wondered is what is energy? And as we've discovered
more and more about energy and different fields, we started to realize that we don't have much
knowledge about what energy actually is. And even Richard Feynman, one of the greatest
physicists of the modern age had this to say. It's important to realize in physics today,
we have no knowledge of what energy is. And so there are some commonalities about energy.
But a lot of it we don't really understand. And what is one of the greatest commonalities
is this conservation of energy. We know that the amount of energy that goes into a system
is equal to the amount of energy that comes out of a system. In other words energy can
neither be created nor destroyed. And that's the one thing that puts all of energy together
into this one group. And so as scientists over time have discovered energy in many different
forms, we've named it in many different areas. And as a result sometimes this alphabet soup
of energy is somewhat confusing. And so I want to make this as simple as I can. And
physicists have done that in the standards. And so when we look at energy, there's really
only three areas where energy is. And so we have energy that is the function of motion.
And so as we have a mass that's moving at a given velocity or to make this simple at
a given speed, it's going to have energy. Energy of motion. And so not only like a car
moving has that, but the particles as they vibrate inside this steel that's really really
hot, is going to be this function of motion. We also have energy that's due to the position
within a field. And remember a field is going to emanate. It could be a gravitational field,
a magnetic field, an electric field. But basically objects are going to have fields around them.
So the earth is going to have gravitational fields around that. And based on where an
object is inside those fields, it's going to have varying amounts of energy. And so
if we were to take a bowling ball and lift it a meter off the ground, it's going to have
more energy due to it's position within that field. And then finally we kind of have a
mishmash of these two where we have radiation. Radiation we know comes to us from the sun.
So it's traveling through space. And really it's vibrations within a field that creates
that energy. And so if you can always thing about energy in these three levels, it's going
to make it a little bit easier to understand. Either a function of motion, position within
a field or finally radiation. And so where should you talk about energy in school? Well
they've left the lower elementary grades intentionally blank. And so you don't have to talk about
it at all. And as they move into third, fourth and fifth, it's pretty simple what they want
you to talk about. And the first thing is that objects, as they're moving, have energy.
And the faster they move, the more energy they have. And so if we had these three objects
here that are colored differently, but if they had the same mass and they were to move.
Which one of those would have more energy? It's going to be the one that's moving the
fastest at any given moment. And you know this. If you were to get hit by a snowball
you'd rather get hit by one that's going really, really slow than one that's going fast. And
that's because it's going to have less energy. Also as you are in elementary school you should
talk about energy being able to be transferred from place to place. In other words energy
can move or it can be transferred from place to place. And it can do that through a couple
of ways. Sound would be one way that we can transfer energy from one place to another.
And so right now the sound is going from your computer to your ears, either through a headphone
or through the air. And so the energy is being transferred from my voice. Also light is transferring
energy from your computer to your eyes. And then finally this is all getting to your computer
through an electrical current. And so there's energy that's moving that to your computer
as well. So you want students to understand that we can transfer energy. You really want
to get away from the idea of saying sound energy or light energy. It's not really that
sound is energy. It has the ability to transfer energy from one place to another. As we move
into middle school then we want to get to this idea, this core idea that energy can
be found as a function of motion. And then as position within a field. And so that function
of motion we tend to refer to as kinetic energy. And so kinetic energy is going to be energy
of objects that have mass. And then they also have a speed or they have a velocity. And
we even have an equation for that. It's 1/2 mv squared, where m is the mass of the object.
We measure that in kilograms. And then velocity is going to be in meters per second. So what
does that mean? The more massive an object is the more kinetic energy it can have as
it's moving. And then the faster it's going the more energy it has. And since this is
a squared value, the velocity is incredibly important as far as kinetic energy. And then
position within a field. We tend to call that potential energy. And so that's your position
within a field. So that could be for example, you know an apple at the top of a tree. There's
going to be gravitational field created by the large mass of the earth. And as we move
that apple up or down we're going to vary the amount of potential energy it has. But
it's not only gravitational. It could be magnetic potential energy. Or it could be electromagnetic.
It could be for example electrons within a solenoid, like we have right here. Then finally
you really want to talk about heat and heat transfer. And so heat, and I put it in quotes
right here, has a couple of different definitions. And so the first one you might think of as
thermal energy due to motion of atoms. And so when you touch a table or you touch an
object and you say that's hot or that's cold, that's one definition. And then the other
definition is energy transfer as a result of conduction, convection or radiation. Now
one of these definitions is correct use in science. And one of them is one that you should
never use. And so in science heat is simply the transfer of energy by conduction, convection
or radiation. We'll talk more about that in the next video. And so if we were to put these
objects right next to each other, there's going to be a transfer of energy from the
hot to the cold. And that's what heat is. When you're referring to this is a hot object
or a cold object, what you're really talking about there is temperature. And temperature
is going to be the average kinetic energy of particles of matter. And so it's important
that the students understand the difference between temperature which is motion of the
molecules. Kinetic energy in the molecules. And then heat, which is going to be a transfer
of energy. As we move into high school we really want to talk about energy. And so the
core thing we want to talk about is the conservation of energy. The amount of energy that moves
into a system is going to equal the amount of energy that moves out of a system. And
so when you drive your car, where does the energy go? Well some people think when you
drive a car you're somehow converting the gasoline into energy. No you're not doing
that. You're taking the energy that was in the gasoline and you're converting it into
another form. In this case a lot of it is going into the motion of your car. But a lot
of it also comes in the form of heat and sound generated by that car. And so the one commonality
of all energy is this idea that energy is conserved. It can be neither created nor destroyed.
And as you move into high school, macroscopically, in other words when we're looking at it from
the big picture you're going to hear tons of different terms related to energy. So mechanical
energy for example talks about all of the energy found within a machine. Or chemical
energy is going to be the energy that can be released within the bonds as we have chemical
reaction. Or electrical energy could be the energy found in a battery. But all of these
at the microscopic level are one of three things. Again energy is simply a function
of motion. A function of position within a field. Or radiation. And if you can keep it
that simple when you're talking about energy and understanding this whole importance of
conservation of energy, then you've got a good start. And I hope that was helpful.