00:00Standing on the scale, the wheel is spinning, and it still weighs 91 kilograms.
00:05You've made your prediction.
00:06Let's see what happens when I throw it up over my head in three, two, one.
00:15What do you think?
00:16I don't know about you, but to me it looked like a shaky mess.
00:20Let's watch that again in slow-mo, and I will graph the scale readings.
00:30As you can see, during the lift, the scale oscillates around 91 kilograms, the same as it read when I was stationary.
00:39So it seems the apparatus doesn't get heavier or lighter when it is lifted while spinning.
00:44The only large deviation from the average comes at the end of the lift, when I let the wheel fall so the scale reading drops,
00:50and then I slow its descent and so the scale reading rises.
00:54So the question remains, if the wheel doesn't get lighter, why does it feel lighter?
00:58This demonstration was first performed by Professor Eric Laithwaite.
01:03Listen to how he describes it.
01:04So here goes 40 pounds of wheel as light as a feather.
01:07This is not a conjuring trick.
01:10This is a fact of science.
01:13He sure makes it look easy, doesn't he?
01:16Watch it again carefully.
01:19A fact about a spinning wheel that so far everyone has missed.
01:25Professor Laithwaite claimed the gyroscope's properties couldn't be fully explained by Newton's laws of motion.
01:32I disagree.
01:33But in order to understand why the wheel feels so light, we first have to consider why it feels heavy when it's not spinning.
01:39So two-handed, that's as far down the shaft as you can hold it?
01:42Yep.
01:42Holding the shaft horizontally, you clearly need to provide an upward force equal to the downward weight of the wheel.
01:48But this is not enough, because with only these two forces, there would be a net torque causing the apparatus to rotate.
01:53So you need to create a counter torque in addition to supporting the weight of the wheel.
01:57This requires pushing down with one hand and pulling up with the other.
02:01And the upward force must be greater than the downward force by an amount equal to the weight of the wheel.
02:05So the force on each of your hands is significantly greater than the weight of the wheel.
02:10Now once the wheel is spinning, the torque due to its weight now causes it to process rather than fall to the ground.
02:16Therefore, no counter torque is necessary.
02:18You only need to supply an upward force equal to the wheel's weight, so it feels lighter.
02:23Now the trick to lifting the wheel over your head is to push it forwards as you release it.
02:28Laithwaite knew this.
02:29If you force a gyroscope to process faster, it lifts up.
02:33Hurry the procession and it rises.
02:37But the weight doesn't change.
02:39Similarly, if you slow the procession of a gyroscope, it goes down.
02:43Slow the procession and it falls.
02:45Dramatically.
02:47I'll show it to you, Rod.
02:49Yeah, I'll show it to you.
02:50It's hard to go back the way that it doesn't want to process.
02:53With two hands.
02:54So you can't say it becomes as light as a feather when it's rising.
03:02It certainly doesn't become as light as a feather.
03:04I can say that too from having felt it.
03:07But it does feel lighter.
03:09And I think maybe part of that has to do with the fact that I'm not having to counter the torque with my hand.
03:15You know, all I have to do is support the weight of the disc,
03:18but I don't need to provide any torque with my hand to counter that gravitational torque,
03:24which is what makes it feel so awkward when you're trying to hold it when it's static.
03:27When you apply a torque, as you were,
03:30then there's a force up on one side of the hand and down on the other side.
03:35And if you decrease the force on both sides, then it will actually feel lighter.
03:41It feels lighter without actually getting lighter.
03:43Yeah, yeah.
03:44What it does is to decrease the apparent weight that you're feeling.
03:54You know, you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're feeling like you're
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