Hi. It's Mr. Andersen and today
I'm going to be talking about physics. Physics
comes from a greek word physis which just
means nature. And so you could argue that
physics is the oldest science that we have.
Because the first time somebody looked up
at the moon and wondered why the moon goes
through its phases, they were doing physics.
And so it's been around thousands of years.
But it really didn't become quantified until
we got to the scientific revolution. One of
the big names is Galileo Galilei. Again he
really was good at using the telescope and
made some amazing discoveries as far as space.
But he also did some studies in mechanics.
Or in kinematics. Or how objects move. He
probably didn't drop those objects from the
Leaning Tower of Pisa. But he did do some
cool experiments on pendulums. And so let
me show you an example of what he did. I'm
using software called phun. Phun is a physics
simulator and it actually is a lot of fun.
What you can do is build objects. And then
you just hit play. And then those objects
will start to move. And so that's a simple
pendulum. One similar to what Galileo was
actually studying. And so let me move back
for a second. And let me make another pendulum
over here. And one of the first things he
discovered is that when you have two pendulums,
we'll say the one on the left and one on the
right. And the one on the right has a longer
length. That one's actually going to have
a longer period. In other words the time it
takes to swing back and forth. He also found
that no matter what the object's weight is,
they have the same period. And so he was starting
to figure out this idea, at least that all
objects seem to swing, if not fall at the
same rate. So let me get rid of some of these.
And clear this off. And now we'll go back
and talk a little bit about the next scientist.
And his name was Isaac Newton. Isaac Newton
came up with three theories. Or three laws.
And you've probably learned these before.
First one is the idea of inertia. And you
have maybe heard it this way. That an object
at rest tends to stay at rest. An object in
motion tends to stay in motion. So we call
that his first law. His second law could be
summarized as this. Force equals mass times
acceleration. And then the last one is this
idea that for every action there's an opposite
and equal reaction. And so we call those reaction
pairs is a good way to say that. As I make
that. In other words when I push on a wall,
a wall is pushing back equally on me. And
so let's jump into the virtual world and take
a look at how those would work. First of all
let me add a ground for just a second. And
so now I'm going to add, let's see. Let's
go back. Actually, so let's add a ground.
And now let me add an object. So let me rewind
for just a second. So if I had a ball like
this and hit play, that object is going to
fall like that. If I rewind it for a second
and I lose gravity. So there's no gravity
and I hit play. What's going to happen? Well
if there's no gravity and I hit play that
object is now at rest and so it's going to
stay at rest. Once I add gravity to it, it's
just going to fall. Now if I time it right,
again I had it bounce. And then I got rid
of gravity and it just kept going in that
direction. If I add gravity again, it's just
going to fall all the way down. And so that's
Newton's First Law. An object in motion stays
in motion. An object at rest is going to stay
at rest. And if you're paying attention down
here, this object is starting to move up because
I got rid of gravity. So we can make it stick
down to the bottom. Okay. What was Newton's
second law? Newton's second law remember is
that force is equal to mass times acceleration.
What does that mean? F=ma. Well it essentially
means that if you apply a force to a small
mass you're going to get a huge acceleration.
Or if you apply a force to a huge mass you're
going to get a small acceleration. So let
me give you an example of that. Let's bring
in a catapult. And so if I bring a catapult
in like this, and hit play. Catapult is going
to throw that object. Oops. I got rid of gravity
for a moment. So it's going to throw that
object in the other direction like that. Let
me rewind that for a second. And so what I
can do is I could grab this little object
right here. And I can change what it's made
up of. And so let's change its mass. And so
now let's not have it be a mass of 60 grams.
Let's make its mass be much bigger. Like 1.5
kilograms. So if I throw it again. Uh . . . It's
not able to throw it. So again what I've done
is I've increased its mass and so its acceleration
got slower. Let's try and find something in
the middle. Let's find a mass that maybe works.
So something like that. And so that would
be Newton's Second Law. In other words as
you increase the mass of an object, that object
is going to, its acceleration is going to
drop off. Now one thing you should have seen
when we did that is don't take a look at the
object this time. But let's take a look at
the catapult. What happens when it . . . did
you see that? So when the object goes to the
right, in this case, then the catapult goes
in the left. And so that's Newton's Third
Law of Motion. For every action there's an
opposite and equal reaction. Now why did the
object go farther than the catapult? That
goes back to Newton's Second Law. Well I'm
getting into a lot of physics and physics
that we'll actually deal with later. But the
reason I'm doing all of that is that I want
you to understand that physics, once we started
quantifying it and we came up with these laws,
it never changed. In other words for the next
two hundred years, once we had Newton's Laws
of Physics, that was it. And in fact in our
book the physics that we cover is just Newtonian
physics. And so what do I mean by that? Well
mechanics. So we're just talking about one
specific type or one part of physics. Mechanics
and all we understood about mechanics dealt
with just this box down here. And so if we
look at the size of objects. And so right
here I'm going from size of objects down at
the level of an atom. So this would be an
atom down here, up to the size of a planet
up here. So if we go from the very small to
the very big classical mechanics or Newtonian
physics only works if you're dealing with
big objects. Like objects the size of me.
Or the objects the size of a catapult. But
when you get down to the level of an atom,
it really didn't make sense. Speed is another
thing. So if we go from speed where we're
not moving, or moving as fast as a bicycle.
And then we move up to the speed of light,
the rules tend to change as well. And so physics
is a really broad science. But we didn't start
to understand this until we started to get
some people. And so Einstein was the first
person to start to explain what happens to
objects, not just swinging on a pendulum but
as they start to move really fast. And as
they move towards the speed of light. And
he found some really crazy stuff. Like as
you start to approach the speed of light,
time will actually slow down for you. In other
words you could travel away from here at the
speed of light and come back. And you and
I are going to be a different age. We also
had, this would be Max Plank. But a lot of
scientists came up with this idea of quantum
mechanics. Quantum mechanics is kind of explaining
what happens at that atomic level. Where we
start to get this duality. Where it's not
only a particle, these small little objects.
But they have properties of waves as well.
And then finally we have in this last century
the arrival of what's called quantum field
theory. Again I could put tons of scientists
with each of these, but this is Richard Feynman
who actually is, it's just fascinating. If
you want to be fascinated by a scientist,
type that into YouTube and you're going to
find some wonderful interviews. But he came
up with these Feynman diagrams to explain
what's going to happen, not only at a high
speed, but at the atomic level. And so what
I want you to understand is that classical
mechanics or Newtonian physics are really
what we're going to talk about for a lot of
the year in physics. But it's just one thin
slice of the pie that is physics. And even
with that, mechanics is one thin slice of
physics. So we're going to deal a lot with
kinematics, like acceleration, motion, graphing.
But there's a whole other groups of physics
in physics called thermodynamics where we
deal with things like heat. There's another
group where we deal with electromagnetism.
So we deal with things like electricity, magnetism
and light and optics. And so I'm leaving some
things off here. Physics also is made up of
a lot of the idea of this quantum theory and
how we move at that small level. And so there's
a lot to physics. But what I want you to understand
is that physics is simply a way to understand
our world. And if you understand that, you've
taken a first step. And so I hope that's helpful.
