Hi. It's Paul Andersen and welcome
to disciplinary core idea PS3C. This is on
the relationship between energy and forces.
And this model right here is Newton's cradle.
And what will happen is as we release this
ball, as long as they all have the same mass,
the energy will be transferred through them.
And it will just move back and forth until
eventually that energy ends up in sound and
heat. And so when objects are touching or
even when they're not touching they can exert
forces on one another and sometimes transfer
energy. And so in review, what are some of
the interaction forces? We can have interaction
forces when objects are touching. Like these
objects right here. There's going to be an
electromagnetic force between the two. It's
keeping one on top of the other. And as we
slide one on top of the other it's going to
generate a frictional force. And that energy
can eventually be transferred into heat. But
objects remember don't have to necessarily
be touching to exert forces on one another.
And that's because of what are called fields.
We could have gravitational fields. Magnetic.
Or even electric fields. And as we move those
objects we're moving the energy within the
field as well. And so let's look at these
two objects. The earth and an apple. There's
going to be a gravitational field between
the apple and the earth. And if we were to
raise that apple we would change that field
within this force. And so we would really
store potential energy within that apple.
And so what we can do is look through a lot
of different scenarios and if we understand
what's going on in fields we can see where
that energy is being transferred. And so let's
look at this one for example. If we have a
simple pendulum. As it is frozen in time,
we've got a certain amount of potential energy.
And that's due to this field, this gravitational
field underneath it between the pendulum and
the earth. And as we release it, it converts
some of that energy into kinetic energy or
energy of motion, and then it stores some
of that as potential energy as well. Or if
we were to look at a bungie jumper. Why does
the bungie jumper fall? It's due to these
fields, gravitational fields that are pulling
it down. But we're converting some of that
energy as it falls down into tensional energy
of the bungie. That's why it doesn't fall
forever. It stores energy in that bungie.
And then it uses some of that energy to move
them up again. Or if we were to look at magnetic
fields, this gyroscopic magnet seems to be
defying gravity. But that's because they're
also magnetic fields in here. And so we have
a north side of the magnet on this side. And
a north side of this large magnet. So it keeps
it kind of levitating above ground. So how
do you teach this in school? In the lower
elementary grades we want to get this idea
across that if you push on something you can
give a velocity or a speed to that. And the
more we push, the greater force we give it,
then the greater the speed is going to be.
Next thing that you should let them know is
that the faster a speed when we have a collision,
equals more change. And so if we were to throw
this red ball against a wall at a low speed,
it's not going to damage it much. But if we
throw it at a faster speed or even a faster
speed we're going to have more change to that
object. As you move up in elementary school
then we want to talk about contact forces
changing motion. In other words when we have
this object on top of this object. As we slide
one past another we're going to start to convert
some of that movement into energy. And that's
a frictional force that's opposing that motion.
But if we drop motion down, the reason it
doesn't fall through that object is because
there's going to be electromagnetic forces
between. But remember, we can have distant
forces that are applying on different objects
as well. And so that spinning gyroscopic magnet,
the reason it's able to levitate is there's
going to be a magnetic force between these
two northern poles of a magnet. As we move
into the middle school then we want to start
talking about the interactions causing transfer
between objects. Or energy transfer. And so
there's a gravitational field between the
apple and the earth. And as we raise that
apple, we're really changing the force of
that field, or the energy contained within
that field. So we're storing energy in the
apple, which we could return as it falls to
earth. Likewise when we're in middle school
we should also add the idea of magnets and
charges. And so if we have two magnets, and
they have opposing poles, there's going to
be an attractive force between these two.
Likewise if we have two charges that have
the same charge, is there's going to be opposition
and it's going to repel each other. And if
we have attracting charges or unequal charges
there are going to be an attractive force
between the two. As we move into high school
we really want to start to quantify that a
little bit. And so when we move objects, when
we change their position and we can really
change their energy. And so be it magnetic,
gravitational or electric fields, as we move
objects the field energy is going to change.
And so the energy within this field changes.
And objects are going to tend to move along
their easiest path. In other words, if we
have two objects that are attracted to one
another, they're going to move towards each
other. They're going to move in a way that
can reduce the amount of field energy. Likewise
if we have two magnetic poles that are going
to oppose each other, they're going to move
away from each other. And that's going to
lessen that field energy as well. Now it's
not as simple as that. Prior motion and forces
can affect the actual direction of motion
as well. But that's the interaction between
forces and energy. You really want to get
your students using this idea of fields to
explain why objects interact with one another
when they're not touching. But I hope that
was helpful.
