[MUSIC PLAYING]
So I got this fancy top called a PhiTOP, which is just
an oblong piece of metal.
But watch what happens when you spin it lying down.
It stands up.
That is, if you start it spinning along its minor axis,
it will rise up and spin along its major axis.
Now, this toy is shiny and pretty,
but that physics trick at the end,
you could make a hard boiled egg stand up like that.
Check it out.
It will even stand up on its smaller end and the best part,
you can spin it and color it with markers.
Perfect way to decorate your Easter eggs.
So it's nothing fancy about this particular toy,
although it does look pretty fancy.
But in both of these spinning behaviors, the center of mass,
that is, the point that pretty much tells you
where the average of the mass is, the point that's supposed
to stay as low to the ground as possible because of gravity,
that point rises up.
It looks like it's not obeying gravity.
So weird.
Almost as weird as this demo.
It seems like the wheel here should just
fall straight down since it's just hanging on the rope.
But it stays sideways.
But still, you ain't seen nothing.
This is the famous Tippe Top.
Not only does the center of mass rise up,
but the whole thing flips over.
If your mind is blown, you're in good company-- well, me.
But also here are two Nobel Prize winners
and quantum physics pioneers playing with the Tippe Top.
Back in the 1950s, there was actually
a craze among physicists to figure out how this toy works.
All these papers just for analyzing these toys,
because their behavior is super complex.
As one scientist put it, "even the most simplified model
for the rolling and gliding TT is
a nonintegrable dynamical system with at least 6 degrees
of freedom."
So why are these toys so weird?
Let's take a crack at the egg.
First, how is energy conserved when it stands up?
Because energy has got to be conserved.
So the rising center of mass means
that gravitational potential energy increases.
Where did that energy come from?
Well, the egg actually slows down a bit,
so kinetic or motion energy is converted
into potential energy.
The egg then also speeds up as it stands up
because of the changing moment of inertia,
but that doesn't affect the energy transfer.
So overall, energy is conserved if you
ignore heat losses to friction, which physicists like to do.
Now, how does the egg stand up?
First, a little physics vocabulary.
When something rotates, it has angular momentum,
which physicists like to define with the right hand rule.
As along the axis it's rotating about,
curl your fingers with the direction of the spin,
and your thumb points along the angular momentum vector.
Angular momentum is just like regular linear momentum.
Something that's moving wants to keep
moving unless there's a force stopping it like friction.
In the same way, this wheel wants
to keep spinning with its angular momentum
vector pointing in the same direction
unless there's a torque stopping it like my hand.
When you apply a torque to something,
that is a force some distance away from whatever you're
going to rotate that thing about,
it can make it spin faster or slower
or change the direction it's spinning.
Put simply, torque wants to increase angular momentum
in the direction of that torque.
Watch this.
Gravity is applying a force here.
Now, this is where it gets confusing,
because just like angular momentum
is defined as not really in the direction that the wheel is
spinning, but out of the spinning plane,
torque is defined as r cross F which, by the right hand rule,
is also in a third direction.
So torque on the wheel like this would increase momentum
in that direction.
Torque this way, like that due to gravity,
would make the angular momentum vector want to rotate that way.
And the gyroscope will turn, what
we call gyroscopic precession.
Now, back to the egg.
It works similar to the wheel's procession.
In fact, the egg processes.
In order for the egg to stand up,
its angular momentum has to change due to a torque.
When the egg starts spinning, it slides
around a bit, which means there's friction
that opposes the sliding.
Friction provides some of the torque
needed to stand the egg up.
Now, we can test that.
If we spin these on a surface that has little to no friction,
they shouldn't behave the same.
Yeah.
It doesn't work the same.
Nope.
You can also try spinning a raw egg, which
doesn't work because the fluid on the inside
doesn't move with the shell.
So it turns out, tops and rotational physics
is pretty complicated.
But you get the coolest phenomena.
Thank you so much for watching this episode of "Physics
Girl," and happy physicsing.
What's that strange A capella music in the background,
you ask?
Well, it's actually a collaboration
I did with the super talented Tim Blais on his channel A
Capella Science.
I dressed up as Isaac Newton and sang
to the tune of "Defying Gravity" from "Wicked."
It's pretty ridiculous, but super fun and educational.
Definitely worth checking out.
So I'll link to that in the Description.
I'm also excited to announce that PBS Digital Studios has
just launched "Crash Course Physics," which is really cool.
It's a great series, great for going back and learning
the basics of physics.
So I will link to that in the Description as well.
Check them both out.
And thank you for watching all the way through the credits.