Hi. It's Mr. Andersen and this is chemistry essentials video 49. It's on the conservation
of energy. If you've ever done any calculations or reading on energy you've noticed that there's
a unit named joules. And that's named after this guy right here, James Prescott Joules.
And he came up with this really innovative way to look at energy transfer. And so in
this apparatus right here what we have is a weight. And that weight is lifted off the
ground. So there's a string attached to it. We have to crank this string all the way up
like that. And then we eventually have this weight at a given height. And so what it has
at this point is potential energy. Gravitation potential energy. And so what Joules was looking
at is how can we convert that to changes in temperature. Or how do we get that energy
transfer through heat? And so what happens in as this weight falls, what it's doing is
it's spinning these blades that are in water and the friction of that spinning of those
blades in water is increasing temperature. And so what he was able to do is make measurements
as to how that mechanical energy or that work of that falling weight is actually transferred
into temperature changes. And so if we're ever talking about conservation a good way
to think about that is a teeter-totter. And so we've got a before and an after. And so
if we've got two systems, so system one and system two, the amount of the energy that
they have before interacting with each other has to be exactly the same as the energy they
have after. And so in a closed system, in other words, if we're looking in just isolation
at these two systems, system one and system two, if system one has more energy than system
two, then we're going to transfer that energy from one to two. And so the energy is going
to be conserved. Now that energy could be energy transferred through heat or it could
be energy transferred through work. So the amount of energy we have before and after
has to be equal or has to be conserved. So before and after that interaction the amount
of energy has to be conserved. So again, system one had more energy to begin with than system
two. There was energy being transferred but the overall energy that we had had to stay
the same. And so where could we apply this? Well look no farther than driving a car. And
so where is most of the energy in a car that drives that car? Well that energy is going
to be in chemical energy. Chemical energy of the gasoline. So in those bonds we have
a certain amount of stored energy. And as we release that through combustion what we're
going to do is transfer that energy into different forms. And so it's all chemical energy to
begin with but as that car moves where are we transferring that energy into? Well we're
transferring a lot of it into mechanical energy. Mechanical energy is driving the piston in
that internal combustion engine. Driving the crankshaft. Driving the drivetrain. Moving
the wheels. And it's moving that car. Now if you've ever put your hand on an engine
you'll notice that it's really hot. So we're also converting a lot of energy into heat.
There's also probably electrical energy inside there. We have light energy perhaps that's
being transferred. And so that amount of energy that we had before and the amount of energy
that we have at the end has to be conserved. We don't either create nor destroy energy.
And so if we go back to our teeter-totter again, the amount of energy that we had before
was mostly chemical energy. But it's being converted into mechanical work, so we're driving
that drivetrain, driving that car, moving that car. We're also transferring a lot of
that energy through heat. We're also producing maybe electrical and light energy. But if
we look on either side, before and after, the amount of energy that we have has to be
conserved. And so did you learn to related the magnitude, how big it is, the type and
the direction of that energy transfer? Remember when I'm talking about type I'm either talking
about energy transfer through heat or energy transfer through work. And then have you learned
this idea of conservation? That the amount of energy that we have before and after have
to be exactly the same. I hope so, and I hope that was helpful.