Standing on the scale.
The wheel is spinning and it still weighs 92 kilograms.
You made the 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 kilograms, 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 Laithwaite.
Listen to how he describes it.
>> So here goes 40 pounds 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 so far everyone has missed.
>> Professor Laithwaite claims 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 is not spinning.
So two handed that is as far down the shaft as you can hold it.
>> Yeah.
>> 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 neck 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 a wheel over your head is to push it forwards as you release
it.
Laithwaite knew this.
If you force a gyroscope to process faster, it lifts up.
>> Higher 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 showed you right?>>
Now show it to me.
>> Hard to go back the way that it doesn’t want to process.
>> [unintelligible]
Now you can’t say it becomes as light as a feather when it is rising.
>> It certainly doesn’t become as light as a feather.
I can say 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 am 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 part, which is what makes it feel so awkward
when you are trying to hold it when it is static.
>> When you apply a torque, as you were, then the 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 take first the apparent weight that you were feeling.