Galileo Galilee is best known for
Galileo Galilee is best known for

his astronomical discoveries with the telescope, but equally important were his
his astronomical discoveries with the telescope, but equally important were his

experiments and discoveries in mechanics: the physics of moving bodies.
experiments and discoveries in mechanics: the physics of moving bodies.

This work, completed late in Galileo's life, was one of the foundations that
This work, completed late in Galileo's life, was one of the foundations that

Isaac Newton, working a generation later, was to use to to build his great synthesis
Isaac Newton, working a generation later, was to use to to build his great synthesis

the culminated in the three laws of motion and the law of universal gravitation.
the culminated in the three laws of motion and the law of universal gravitation.

In this demonstration,
In this demonstration,

we will be exploring one of Galileo's important discoveries
we will be exploring one of Galileo's important discoveries

about the behavior of massive bodies freely falling in a gravitational field.
about the behavior of massive bodies freely falling in a gravitational field.

To Galileo's contemporaries,
To Galileo's contemporaries,

the behavior of a mass of body is very easy to understand.
the behavior of a mass of body is very easy to understand.

It's made of the earth.
It's made of the earth.

And just like Aristotle told them, 2000 years before in his great work of physics,
And just like Aristotle told them, 2000 years before in his great work of physics,

because an object is made of the earth, if we drop it from a height, it is following
because an object is made of the earth, if we drop it from a height, it is following

it's natural tendency to settle down into the rest of the mass of the earth.
it's natural tendency to settle down into the rest of the mass of the earth.

Furthermore, the heavier an object the greater that is to fall to the ground.
Furthermore, the heavier an object the greater that is to fall to the ground.

So a heavy object, like this two kilogram hammer,
So a heavy object, like this two kilogram hammer,

should actually fall faster than this half a kilogram hammer.
should actually fall faster than this half a kilogram hammer.

When I hold the hammer and
When I hold the hammer and

drop it, the speed with which it falls depends upon how much mass there is.
drop it, the speed with which it falls depends upon how much mass there is.

But is this true?
But is this true?

Galileo tested this assertion in a series of very simple experiments.
Galileo tested this assertion in a series of very simple experiments.

We're going to do those experiments here using the same pari of hammers.
We're going to do those experiments here using the same pari of hammers.

This one weighs two kilograms,
This one weighs two kilograms,

this one weighs half a kilogram,s o the mass ration is four to one.
this one weighs half a kilogram,s o the mass ration is four to one.

I'll give myself a little height here, I'm going to hold them up and drop them at
I'll give myself a little height here, I'm going to hold them up and drop them at

the same time Aristotle would predict that the heavier hammer would fall the fastest
the same time Aristotle would predict that the heavier hammer would fall the fastest

and hit the ground first, and the lighter hammer following shortly behind, but
and hit the ground first, and the lighter hammer following shortly behind, but

what really happens, let's not rely on the words of Aristotle.
what really happens, let's not rely on the words of Aristotle.

Let's do what Galileo did and
Let's do what Galileo did and

do the experiment, two kilograms, half a kilogram, four to one mass ratio.
do the experiment, two kilograms, half a kilogram, four to one mass ratio.

Which one will hit the ground first, the heavier one according to Aristotle or
Which one will hit the ground first, the heavier one according to Aristotle or

something else?
something else?

Lets see.
Lets see.

[SOUND] They both hit the ground at exactly the same time,
[SOUND] They both hit the ground at exactly the same time,

now you might argue four to one isn't big enough.
now you might argue four to one isn't big enough.

Well let's go bigger than four to one, let's go 75 to 1.
Well let's go bigger than four to one, let's go 75 to 1.

One kilogram and 75 times less, appropriately,
One kilogram and 75 times less, appropriately,

a little moon ball, and we'll drop them.
a little moon ball, and we'll drop them.

[SOUND] They hit the ground at the same time.
[SOUND] They hit the ground at the same time.

What if we go even lighter?
What if we go even lighter?

Well, let's go to the ratio of 4,000 to one.
Well, let's go to the ratio of 4,000 to one.

This turkey feather, weighs half a gram; 4,000 times less than the hammer.
This turkey feather, weighs half a gram; 4,000 times less than the hammer.

What's going to happen when I drop them together?
What's going to happen when I drop them together?

[SOUND] Behave differently.
[SOUND] Behave differently.

Why?
Why?

Because the feather's so light, that air resistance played an important role.
Because the feather's so light, that air resistance played an important role.

I would like to be able to drop a hammer and a feather, but
I would like to be able to drop a hammer and a feather, but

without the role of air resistance.
without the role of air resistance.

We can't do that easily on Earth, but Galileo could imagine a place where there
We can't do that easily on Earth, but Galileo could imagine a place where there

was no air, and do the experiment as a thought experiment.
was no air, and do the experiment as a thought experiment.

But we don't have to just do it as a thought of experiment.
But we don't have to just do it as a thought of experiment.

In 1971, astronaut Scott did it for the moon in Apollo 15.
In 1971, astronaut Scott did it for the moon in Apollo 15.

>> Well in my left hand, I have a feather in my right hand, a hammer.
>> Well in my left hand, I have a feather in my right hand, a hammer.

I guess one of the reasons we got here today was because of
I guess one of the reasons we got here today was because of

a gentleman named Galileo a long time ago,
a gentleman named Galileo a long time ago,

who made a rather significant discovery about falling objects in gravity fields.
who made a rather significant discovery about falling objects in gravity fields.

And we thought that where would be a better place to confirm his findings than
And we thought that where would be a better place to confirm his findings than

on the moon, and so we thought we'd try it here for you, and
on the moon, and so we thought we'd try it here for you, and

the feather happens to be, appropriately a falcon feather for our falcon.
the feather happens to be, appropriately a falcon feather for our falcon.

I'm going to drop the two of them here,
I'm going to drop the two of them here,

and hopefully, they'll hit the ground at the same time.
and hopefully, they'll hit the ground at the same time.

How about that?
How about that?

[INAUDIBLE] it proves that Mr.
[INAUDIBLE] it proves that Mr.

Galileo was correct in his findings [NOISE]
Galileo was correct in his findings [NOISE]