Kind: captions
Language: en
Now I want you to make a prediction. In
my left hand I have a standard size
basketball and in my right hand a 5 kg
medicine ball. If I drop them both at
exactly the same time, which one will
hit the ground first?
Ah, this is a trick one, isn't it? The
heavy will go down first.
Well, yeah, it'll drop faster. They'll
both hit the ground at the same time.
Give me a
I actually would have thought this one
would go faster cuz it's heavier.
Maybe it's that one.
Maybe this one. Yeah.
So, you reckon this will be faster?
That one will be faster. So, why does
that make it go faster?
Uh, cuz it the weight pulls it down
quicker.
What are we measuring when we say, "Oh,
it's heavier." What are we feeling?
Gravity.
Gravity. [laughter]
Go ahead. Yeah, that's cool.
Objects being pulled to the earth, I
guess.
Okay. So, which of these objects is
being more pulled to the earth? This
one.
That one. The black one.
All right. Well, here's what we're going
to do. I want you to hold both of those
above your head.
You
get really high. Can you [laughter]
Count on a count of three. Ready? 3 2 1
Exactly the same.
They fell at the same time.
Exactly the same time.
They did at the same time.
Was that what you expected to see?
No.
So, what do you make of that?
I need to go read more books.
Magic.
Gravity is going to pull at the same
rate no matter how heavy or how light it
is.
But gravity is how light or how heavy
something is. It's one big massive mind.
[laughter]
There must be some force that's that's
dragging it down. And actually the
actual weight of it doesn't mean doesn't
matter.
Something to do with mass or something.
I can't remember why.
It's almost like the weight holds it
back in a way. Even though that doesn't
seem to make sense.
I think you might be hitting on an
interesting point there. Weight holds it
back. Now, it's not actually weight that
holds it back, but inertia. That's the
tendency of matter to maintain its state
of motion. So to remain at rest if
stationary or to continue with constant
velocity when in motion. What's the big
idea?
The big idea is this one has more mass.
So it's got more weight, which you can
clearly feel, but it's also got more
inertia, which means it's also more
sluggish.
It tends to resist acceleration.
So that greater force is required to
accelerate it at the same rate as this
ball.
Like a heavy car trying to accelerate.
You need more force to get it going.
Exactly. So, what does all that mean?
Well, the force on the medicine ball is
greater than the force on the
basketball, but it has more inertia. And
what's really important is that the
ratio of force to inertia is the same
for all objects. So, everything
accelerates at the same rate and lands
at the same time.
[music]
And the plastic block because it's
conducting the heat to the ice cube
faster. Most of us have been captivated
by one of these, a slinky. [music]