This video is sponsored by brilliant.org This is a really big pendulum and unlike
the pendulum in a clock this Foucault pendulum at the University of Puget
Sound is free to swing in any direction. It takes about eight seconds for it to
go from there over to here and back, but that's not the motion that I want to
show you. Now, this is not an interactive exhibit, but I have special permission.
The motion I want to show you is too slow for you to see, so I'm going to
speed things up in this video about 480 times so that you only see the pendulum
when it's at this point in its swing, here. And doing that will compress the
next 32 hours into four minutes of video. We're going to try science! Played back
at this speed the pendulum appears to move around the room, but that doesn't
really grasp what's really happening, because the ground is what's moving. It's
rotating. You are watching the world turn. Let me explain the pendulum ticks back
and forth due to the law of inertia, which states that an object in motion
stays in motion unless something acts on it. So the pendulum continues to swing
along this plane of motion, and from its point of view it's just swinging back
and forth along that same plane. From the pendulums point of view that ground is
what's moving. Now while that's incredible, if you ask me, it can also be
hard to grasp. So I want you to picture this: a Foucault pendulum placed at the
North Pole would appear to complete a clockwise circle once every 24 hours as
the earth completes a day by rotating beneath it. But that isn't always the
case because at the poles the relative rotation between a pendulum and the
Earth's axis is at its maximum so the closer you move a pendulum towards the
equator the longer it takes for a so-called "pendulum day" to take place
(that's the amount of time at for a Foucault pendulum to move around
the room as it were). Here at the University of Puget Sound a pendulum day
is about thirty two point three hours long. Now the reason it is in twenty four
hours here is because the earth is a sphere. So, the closer you put a pendulum
to the equator the further it is from the Earth's axis and the greater the
difference in angle between the Earth's axis and the plane that the pendulum is
on the greater that differences the less relative rotation there is between the
pendulum and the earth so it takes at least 24 hours to see one pendulum day
and potentially much longer. You can actually figure out your latitude just
by watching and timing a pendulum as it moves in this way but of course there's
easier ways to do that. It's now 5:30 in the morning but I'm awake and ready to
get back at it. At the equator a pendulum day lasts forever.That's because at
that location a pendulum is perpendicular to the axis of rotation
the planet and the pendulums plane are not moving in relation to one another.
Here in the northern hemisphere Foucault pendulum rotate clockwise because of the
Earth's rotation, and that rotation also causes sundial shadows to move clockwise.
I mean it's probably where we got the term 'clockwise' in the first place. If we
put a pendulum at the South Pole it goes counterclockwise, but again it takes 24
hours. We talk about the Sun rising and setting,
but that only appears to happen because of Earth's rotation. And up until this
experiment was done we could only assume that the earth was spinning due to our
observations of the Sun, of the Moon, and of the Stars. But no one had figured out
how to do an experiment to actually test that until 1851 when a physicist named
Leon Foucault came up with this. And that provided the very first simple proof
that the Earth rotates. He did all of that using nothing but a pendulum, and if
you ask me that is pretty remarkable. And that is a pendulum day, now it's worth
noting that most Foucault pendulums on display like this one
have an electromagnet at the top, but that's just to keep them going forever.
You could just use a normal pendulum to do this experiment and get the same
results it just wouldn't last as long, and maybe that's a good thing, cuz this
took me a long time. Making this video took math engineering physics and a lot
of effort. And I put in that effort so that I might inspire you to learn more
about this incredible world around us and that is why I've teamed up with
brilliant dot org to help make that possible. Brilliant focuses on problem-based
learning and I really like that because I know that studies show that solving
problems is one of the most effective ways to learn things. It's also just fun
everyday they release several daily problems in math, science, computer
science, and engineering, and from those you can go deeper into an interactive
course. And there's a recent daily problem on brilliant that I really like
about the physics of how to water your plants while you're away - and it turns
out that there's a much simpler solution to that than building a robotic cactus
watering machine like I did. So, whether you want to learn more about the physics
of everyday life, get better at math in ways that's actually useful, or just want
to expand your horizons go to brilliant.org/kurtis and finish your day a
little smarter. The first 200 of you to do so will also get 20% off of the
annual subscription and gain access to all the daily problems in their archives,
as well as the problem solving courses. Also, using that link will let them know
that I sent you which I would really appreciate, so please check it out! And as
always, thanks so much for watching. Also I want to give a thanks to the
University of Puget Sound for letting me literally camp out beneath their
pendulum. And for those of you that are new here: if you press subscribe you will
add a literal drop of water to one of these plants and that's all that's
keeping them alive.