Kind: captions
Language: en
Standing on the scale, the wheel is
spinning and it still weighs 91 kg.
You've made your prediction. Let's see
what happens when I throw it up over my
head in three, two,
one. What do you think? I don't know
about you, but to me it looked like a
shaky mess. Let's watch that again in
slow-mo, and I will graph the scale
readings.
As you can see, during the lift, the
scale oscillates around 91 kg, the same
as it read when I was stationary. So, it
seems the apparatus doesn't get heavier
or lighter when it is lifted while
spinning. The only large deviation from
the average comes at the end of the lift
when I let the wheel fall so the scale
reading drops and then I slow its
descent and so the scale reading rises.
So the question remains, if the wheel
doesn't get lighter, why does it feel
lighter? This demonstration was first
performed by Professor Eric Leweight.
Listen to how he describes it. So here
goes 40 lb of wheel as light as a
feather. This is not a conjuring trick.
This is a fact of science.
He sure makes it look easy, doesn't he?
Watch it again
carefully. a fact about a spinning
wheel that so far everyone has missed.
Professor Laithweight claimed the
gyroscope's properties couldn't be fully
explained by Newton's laws of motion. I
disagree. But in order to understand why
the wheel feels so light, we first have
to consider why it feels heavy when it's
not spinning. So two-handed, that's as
far down the shaft as you can hold it.
Yep. Holding the shaft horizontally, you
clearly need to provide an upward force
equal to the downward weight of the
wheel. But this is not enough because
with only these two forces, there would
be a net torque causing the apparatus to
rotate. So you need to create a counter
torque in addition to supporting the
weight of the wheel. This requires
pushing down with one hand and pulling
up with the other. And the upward force
must be greater than the downward force
by an amount equal to the weight of the
wheel. So the force on each of your
hands is significantly greater than the
weight of the wheel. Now once the wheel
is spinning, the torque due to its
weight now causes it to process rather
than fall to the ground. Therefore, no
counter torque is necessary. You only
need to supply an upward force equal to
the wheel's weight so it feels lighter.
Now, the trick to lifting the wheel over
your head is to push it forwards as you
release it. Laithweight knew this. If
you force a gyroscope to process faster,
it lifts up. Hurry the procession and it
rises.
But the weight doesn't change.
Similarly, if you slow the procession of
a gyroscope, it goes down. slow the
procession and it falls dramatically.
I'll show it to you, Rod. I'll show it
to you. It's hard to go back the way
that it doesn't want to process two
hands.
So, you can't say it becomes as light as
a
feather when it's rising. It certainly
doesn't become as light as a feather. I
can say that that too from having felt
it. But it does feel lighter. And I
think maybe part of that has to do with
the fact that I'm not having to counter
the torque with my hand. You know, all I
have to do is support the weight of the
disc, but I don't need to provide any
torque with my hand to counter that
gravitational torque, which is what
makes it feel so awkward when you're
trying to hold it when it's static. When
you apply a torque as you were, then
there's a force up on one side of the
hand and down on the other side. And if
you decrease the force on both sides,
then it will actually feel lighter. It
feels lighter without actually getting
lighter. Yeah. Yeah. What it does is to
decrease the apparent weight that you're
feeling.