Kind: captions
Language: en
There are a lot of misconceptions out
there and this is a video about one of
the most common ones. So I went around
asking people what makes the moon go
around the earth and they told me
the earth puts a gravitational force on
the moon.
But does the moon put a gravitational
pull on the earth?
I know
pull on the earth. Yes, it does. Hence
we have tides etc. The moon pulls on the
earth too. It affects like the tides and
women and
it does very powerful.
Does the moon pull on the earth?
Probably that as well. Yeah. So, what I
want to know is uh how does that force
that the moon exerts on the earth? How
does that compare in terms of size to
the force the earth exerts on the moon?
Well, I'm no scientist, but I think that
one would be more powerful than that
one. It's got a greater force coming
from the Earth cuz it's a greater mass
because the Earth probably has more mass
cuz it's a bigger mass. I thought
greater mass is more equals more force.
Does the moon pull on the Earth?
Yes, but a lot less.
Yeah, not as much as the Earth pulls on
the moon.
Yeah, but a little bit.
Not very strongly.
Yes, but much much much much smaller
because of its mass less mass size
because it's smaller. It's much smaller
than than the Earth.
Because it's smaller. Is it small?
Allow me to let you in on a little
secret. Everyone got it wrong. The force
that attracts the moon to the earth is
exactly the same size as the force that
attracts the earth to the moon.
So what's going on here? Why did
everyone get it wrong? Well, I think it
comes down to cause and effect. The
effect of the force on the moon is quite
clear. The moon goes in circles around
the earth. But the effect of that force
on the earth is basically negligible.
The earth barely wobbles at all. So
people interpret this negligible effect
as indicating there's very little force
affecting the earth. But that is
forgetting the third key piece of the
puzzle which is inertia. Inertia is the
tendency of mass to maintain its state
of motion. Since the Earth has a greater
mass, it has a greater inertia. And so
even with the same amount of force on
it, it doesn't accelerate that much.
Now, the funny thing is many of the
people I interviewed could state
Newton's third law, which is every force
has
Oh, an equal and opposite reaction.
Something about Newton's law doesn't
seem to fit into that.
You're good at this. Which Newton's law
are we talking about? the whole equal
and opposite force thing.
Yeah, that one.
So, tell me what you're thinking now.
Uh, well, did one would think that if
the Earth is putting a force on me, I
would be putting an equal force upon it.
So, why didn't they apply it to this
problem?
Well, I think they may have memorized
the words, but not really believe
Newton's third law in their core. Did
they really feel it in their spleen?
I don't think they did. So allow me to
try to convince you all of you spleen
included that Newton's third law really
is true. Let's consider two objects.
Initially they have the same mass 1 kg
each. So obviously the gravitational
force of attraction must be the same on
both of the objects.
Now let's add a second kilogram to the
first object. the force on the second
object will now be twice as great
because that 1 kilogram is attracted
equally to each of the kilograms in the
first object. But what is often
forgotten is that new kilogram is also
attracted to the second object. Meaning
that the total force on each object is
still the same. They're attracted to
each other with an equal and opposite
force.
We could add a third kilogram and we
would find the same thing. The force on
both objects is still the same even
though the object on the left has three
times the mass of the object on the
right. So we can see that no matter what
the mass, any two objects will have the
same gravitational force towards each
other.
Can you feel Newton's third law in your
spleen now? It should settle inside you
and become a part of you.