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The Forgotten Mystery of Inertia

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Re: The Forgotten Mystery of Inertia

#101

Post by scatters »

empath75 wrote: post #94
sopooneo wrote: post #41

A drunk awakens in a void and finds his arms, legs, in fact all extremities are bing pulled outward by some reverse gravity. It is quite unpleasant. By some strange mechanism he is able to make himself start spinning. At first it is worse: in one direction the reverse gravity increases in effect! So he reverses and is relieved to find that in the other it slowly abates. Though the sweet relief is strange. Because if…

would it be possible for a drunk in a void to change his rotation?

No, because angular momentum is conserved, assuming flat space. It is possible to change one's orientation, however.

Re: The Forgotten Mystery of Inertia

#102

Post by bawana »

that a spinning gyroscope does not topple has not much to do with Mach, Einstein, the universe or any such big idea. I can explain it much more simply.

Consider a gyroscope spinning fast. so if all of a sudden you try a push its top northward then that instantaneous force pushes down on the north edge of the disk and up on the south edge.Those specific parts of the disk acquire momentum. However because the disk is spinning, the part of the disk that was north soon becomes south. and the southern piece that was moving up is now north. now the momenta of the influenced disk segments act to right the gyroscope. The same effect can occur during the acceleration of a gyroscope in a missile in space. Even tho there is no gravity. The effect of acceleration on the gyroscope is the same, causing it to maintain its orientation in space. The faster a gyroscope spins, the more quickly it rights itself. and thus appears more stable. as it slows down, the righting effect fails.

Angular momentum is a man made calculation and the upward pointing arrow is really just a make believe thing. If it were a real force, the whole gyroscope should float upwards. LOL. It is a shorthand to represent the average momenta of the influenced parts of the gyroscope.

Re: The Forgotten Mystery of Inertia

#103

Post by philipov »

randallsquared wrote: post #100
librexpr wrote: post #63

Earlier quoted context omitted.

I don't think a point can rotate. What would it mean if it did? There would be no observable change. So no, I don't think the absolute center point moves. From a physical standpoint, though, if you wanted to talk about the absolute center point, you'd have to talk about the lowest level of particles, which gets into the weirdness of quantum mechanics (or maybe a lower level exists?). At that point, I really couldn't…

The most fundamental particle can't rotate, because that would imply that parts of it had different velocities from other parts... but it doesn't have parts at all, by initial definition. So, Democritus' atoms imply that rotation is not a fundamental motion. I think every attempt to visualize this which imagines a single object rotating is doomed. Rotation inherently implies a difference in velocities, and some attra…

Okay, then explain Spin. Angular momentum is defined by how a particle responds to fields, not by the relation of its parts.

Re: The Forgotten Mystery of Inertia

#104

Post by CydeWeys »

empath75 wrote: post #94
sopooneo wrote: post #41

A drunk awakens in a void and finds his arms, legs, in fact all extremities are bing pulled outward by some reverse gravity. It is quite unpleasant. By some strange mechanism he is able to make himself start spinning. At first it is worse: in one direction the reverse gravity increases in effect! So he reverses and is relieved to find that in the other it slowly abates. Though the sweet relief is strange. Because if…

would it be possible for a drunk in a void to change his rotation?

The story is phrased in a way that is delicately subtle, and thus elides the mechanism whereby the drunk can change his rotation.

Here's a hint: It's relevant that the person is drunk. Another hint: Newton's third law.

Re: The Forgotten Mystery of Inertia

#105

Post by mannykannot »

bawana wrote: post #98
mannykannot wrote: post #81

Earlier quoted context omitted.

If each particle is only tethered to the center, how does the circle bring it down again? If the tethers are all fixed to one another, we're back to rigidity. Edit: I'm trying to think of a way to bring in angular momentum without having to derive it in full generality...

a spinning disk 'averages' its mass distribution. Consider a gyroscope spinning fast. so if all of a sudden you try a push its top northward then that instantaneous force pushes down on the north edge of the disk and up on the south edge.Those specific parts of the disk acquire momentum. However because the disk is spinning, the part of the disk that was north soon becomes south. and the southern piece that was movin…

Yes, though I think you can avoid the question of why just "those specific parts of the disk" by considering a dumbbell (two joined, point masses spinning around an axis perpendicular to the center of the rod joining them) rather than a disk or ring, and a continuous torque. If you are pushing northwards on the axis, the maximum rate of change of the instantaneous velocities of the point masses is when they are aligned north-south, and when they are aligned east-west, there is no change in their instantaneous velocity from the applied torque. Integrate this over one revolution, and you get the axis tipping in the east-west plane. A picture would really help, maybe I can find one on the web...

Re: The Forgotten Mystery of Inertia

#106

Post by madaxe_again »

philipov wrote: post #99
dmikalova wrote: post #97

Earlier quoted context omitted.

You could blow in one direction or the other, at an angle. The air you push away will push you the other way.

If you're suspended in a fluid or gas, you're not in a void.

Well, if he had a lungful if air, blowing would work - after all, rockets do work in a vacuum.

That said, he’s drunk, so the answer is to piss into the luminiferous aether.

Re: The Forgotten Mystery of Inertia

#107

Post by madaxe_again »

CydeWeys wrote: post #104
empath75 wrote: post #94

Earlier quoted context omitted.

would it be possible for a drunk in a void to change his rotation?

The story is phrased in a way that is delicately subtle, and thus elides the mechanism whereby the drunk can change his rotation. Here's a hint: It's relevant that the person is drunk. Another hint: Newton's third law.

I call it my inbuilt vectoring urea reaction engine.

Re: The Forgotten Mystery of Inertia

#108

Post by bawana »

mikeash wrote: post #93
mannykannot wrote: post #81

Earlier quoted context omitted.

If each particle is only tethered to the center, how does the circle bring it down again? If the tethers are all fixed to one another, we're back to rigidity. Edit: I'm trying to think of a way to bring in angular momentum without having to derive it in full generality...

You could imagine that they’re connected to the center of rotation with a string or something. You just need centripetal force, not a rigid connection to anything. Although that may still be more than what you’re after....

string held taught by centripetal force is rigid. effect is the same.

Re: The Forgotten Mystery of Inertia

#109

Post by jfhufl »

apsophus wrote: post #36
letlambda wrote: post #24

Earlier quoted context omitted.

Walk around to the opposite side of the gyro wheel. If the acceleration is due to the rotation of the gyroscope, it still points out radially. If it was due to a mass out beyond the rim, you're falling on your head.

What if the mass is distributed in a ring surrounding the gyro at a distance? How would you distinguish between spinning versus mass in that case? General Relativity may seem counterintuitive, but experimentally it really does seem to be the way our universe works. Starting out from the position that absolute motion is meaningless has proven remarkably fruitful. It's also something a lot of very smart people have bee…

Seems to me the main difference is that all the particles in the gyro are trying to go in a straight line, but can't due to being a part of a rigid structure. You should be able to tell the difference by dropping a ball bearing. It will land "straight down" if it's gravity, but move "to the side" if it's rotating.
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