[Jaaanosik (OP)]

A bicycle and a spinning office chair would be enough to put aside this silly idea of a braked wheel experiencing a force in the direction of L.

He hasn't explicitly mentioned that since post 252.

Still trolling however. Most recent post had at least four errors, one of which was the lack of direct relevance of the videos to the situation being discussed.
I find it best to just not feed the trolls. He's not here to learn anything, only to push our collective buttons and get his jollies from those who continue to respond.

I try to respond to intelligent questions, but the last several post have neither asked questions nor displayed any deliberate intelligence.

Halc,
Please, point the errors or otherwise your posts are trolling,
Jano

[Halc]

Please, point the errors or otherwise your posts are trolling,

Error 6: Failure to respond to a troll is not in itself trolling. It is doing the troll and the rest of the world a service, similar to abstinence of feeding wild geese.
If you wish a response, show some intelligence in your posts, not goose droppings.

The torque is a real force

1: Continued equivocation of force and torque, despite numerous posts informing you of this error.

during the braking of the wheel otherwise we would not have the gyro precession.

2: Braking of the wheel does not cause gyro precession.

https:  //www.youtube.com/watch?v=qS_dcNqs3d4
Physics - Mechanics: The Gyroscope (3 of 5) The Torque of a Spinning Gyroscope

3: Link to a video about gyro precession, when the topic at hand concerned the braking of a spinning wheel. A) Your example does not involve precession, and B) The video lacks any mention of the wheel being braked or otherwise slowed.

The top view of the wheel. The darker gray balls represent two centers of mass of two halves of the wheel.
The orange vectors are torques positioned at the same position as in the second video.

4: The second video does not depict any masses as two separate centers of mass. These two separate masses play no significant role in the situation at hand. In particular, the angular moment of an object is not a function of the mass and separation of those two centers of mass.

5: Your orange vectors are shown parallel to the disk axis, but in the video the one vector shown is perpendicular to the axis of rotation of the disk. This is not the 'same position', evidence of the irrelevancy of your choice of videos to the topic you're trying to discuss.

OK, more than 4.

[Jaaanosik (OP)]

Please, point the errors or otherwise your posts are trolling,

Error 6: Failure to respond to a troll is not in itself trolling. It is doing the troll and the rest of the world a service, similar to abstinence of feeding wild geese.
If you wish a response, show some intelligence in your posts, not goose droppings.

The torque is a real force

1: Continued equivocation of force and torque, despite numerous posts informing you of this error.

during the braking of the wheel otherwise we would not have the gyro precession.

2: Braking of the wheel does not cause gyro precession.
...

Halc,
I'd like to answer 1 and 2 first.

1.

If torque is not a real force then what is preventing the guy to rotate the wheel against the torque (precession direction) at 2:50 min in this video?


2.




The arm (r) of the assembly is like a spoke of a bigger 'wheel'.
The rotation of this 'virtual wheel' is in the F=mg direction, down.
The gyro wheel angular momentum L is 'breaking', preventing the free fall, this generates the torque.
If we increase the mass at the end of the gyro wheel then the angular momentum 'brakes' more, bigger torque, faster precession,
Jano

[Halc]

I'd like to answer 1 and 2 first.

Continued equivocation of force and torque

If torque is not a real force then what is preventing the guy to rotate the wheel against the torque (precession direction) at 2:50 min in this video?

At 2:50 the guy is just hefting the thing around to show that it's heavy.  I'm guessing the object to weigh about 150 Newtons.  Were he to stand still for a moment holding it like that, he seems to be applying about 300 N upward with his right arm, 150 N downward with his left, and gravity supplying the remaining 150 N of weight downward.  That's a net force of zero which means it doesn't accelerate either towards the ground or the sky.
On the torque front, the torces applied at the various points along its length add up to zero torque, which is why the thing doesn't begin to rotate while he's holding it.

At 3.04 it show him holding the spinning object to the right.  It has zero momentum, zero angular momentum in the direction of the camera (the one we're using, not the other camera in the picture), and positive angular momentum to the left. I'll consider the 5 seconds from that moment, after which the spinning object points at the camera.

Force: For the duration, the guy supplies 150N upward and gravity 150N downward, hence the thing doesn't acquire significant momentum upward or downward.  He varies it a bit as he lifts the thing over his head, but the net momentum remains zero. Were he to stop applying this force, there would a net downward force and the object would accelerate to the ground.

Torque:  He (and gravity) apply about 150 N-m of torque to the object, initially in the direction away from the camera.  Sure enough, the object has something like 600 Nm²/sec angular momentum in the direction away from the camera after those 5 seconds, but has not moved away from the camera since torque is not force.  Similarly, as we approach time 3:09, he (and gravity) are applying about 150 N-m of torque to the right, which by 3:09 has entirely cancelled the angular momentum to the left it initially had.

The two (force and torque) are totally separate things, and have totally separate effects. Your continued equivocation of them is a serious error.

2: Braking of the wheel does not cause gyro precession.

The arm (r) of the assembly is like a spoke of a bigger 'wheel'.
The rotation of this 'virtual wheel' is in the F=mg direction, down.

Again you equivocate force and torque.  Yes, the forces being applied result in torque on the assembly, but torque doesn't make something move down, net force does, and there is no net downward force in the scenario depicted.  It has no reason to move downward.

The gyro wheel angular momentum L is 'breaking', preventing the free fall, this generates the torque.

Braking requires motion and friction resisting (slowing) that motion. There is no downward motion to resist in this situation, and the assembly is assumed to be free of friction. Yes, toy gyros slow over time and eventually fall.  The ones in space stations run in a vacuum and do so for years. There's nothing being slowed down, hence the video does not depict your 'braking' scenario where energy is being dissipated by friction. It is an irrelevant choice of videos to make the (incorrect) point you were attempting.

Of course, posting an irrelevant video obfuscates your point, which serves the purpose of being a troll, so it all depends on what your goals are in the making of that selection.

[Jaaanosik (OP)]

...

The gyro wheel angular momentum L is 'breaking', preventing the free fall, this generates the torque.

Braking requires motion and friction resisting (slowing) that motion. There is no downward motion to resist in this situation, and the assembly is assumed to be free of friction. Yes, toy gyros slow over time and eventually fall.  The ones in space stations run in a vacuum and do so for years. There's nothing being slowed down, hence the video does not depict your 'braking' scenario where energy is being dissipated by friction. It is an irrelevant choice of videos to make the (incorrect) point you were attempting.
...

Halc,
The torque is a rotational inertia multiplied by an angular acceleration.
There is a torque therefore there has to be an angular acceleration.
Please, show us, where is the angular acceleration so we can have the torque?
The gravitational acceleration g is not the angular acceleration because it is in a different direction.
Where is the angular acceleration?
Jano

[Halc]

The torque is a rotational inertia multiplied by an angular acceleration.
There is a torque therefore there has to be an angular acceleration.
Please, show us, where is the angular acceleration so we can have the torque?

Read my 4th paragraph in the previous reply, which answers exactly this. It shows the resulting angular acceleration.

[Jaaanosik (OP)]

The torque is a rotational inertia multiplied by an angular acceleration.
There is a torque therefore there has to be an angular acceleration.
Please, show us, where is the angular acceleration so we can have the torque?

Read my 4th paragraph in the previous reply, which answers exactly this. It shows the resulting angular acceleration.

Halc,
the guy in the video cannot turn counter clockwise at 2:50 min and but he can turn clockwise at 2:55 min without any problem.
There is NO change in the setup, just his intention where to turn.
What is the delta?
Is he wrestling with a force at 2:50? Inertial force to be accurate?
This is very important to settle.
Also going back, where is that angular acceleration? This does not explain it.
Jano

[Jaaanosik (OP)]

Halc,
I understand your argument about the units of measure for the torque - Nm.
One way to look at it - a force applied/generated at a distance from the axis.
It is an inertial force.
If torque is not a force at a distance from the axis then F=mg is not a force as well.
Right, it is just what people use to actually calculate motion but it is not real force, gravity is a curvature of space-time.
The centripetal force is real but the centrifugal force is not real.
Going on a centripetal/centrifugal ride in a park and having 10 kilo brick in one's lap to check the centrifugal force would not be fun,
Jano

[Jaaanosik (OP)]

Hi all,
when a gyro wheel spins, nothing happens.
The wheel has an angular momentum and it is a stable vector.
Minute 48 in this video:

Do we need a force, some work done to rotate the angular momentum, to rotate the gyro wheel axle?
Jano

[Jaaanosik (OP)]

Hi all,
Minute 29 of the same "8.01x - Lect 24 - Rolling Motion, Gyroscopes, VERY NON-INTUITIVE video."
Professor Lewin says: "There is no net force on that wheel, but there is a net torque."
What is a net torque? Out of nothing?
We can see, that if the torque is not there then there is no precession, minute 48.
The wheel is stable, no net force without the additional weight on the axle.
Also the wheel is stable no net force with the additional weight on the axle with the precession.
That is peculiar.
What are the causes of the precession effect?
The external torque on the angular momentum of a rotating wheel.
Both are required, if one is missing then there is no precession.
Jano

 

[Halc]

I didn't respond to several posts due to obvious lack of reading prior responses.
You're still assuming that force is torque, which is going to give you wrong answers every time.

Professor Lewin says: "There is no net force on that wheel, but there is a net torque."
What is a net torque? Out of nothing?

Net torque means that the sum of the torque vectors acting on the wheel is nonzero.  No, those torques must be transferred to the wheel.  Conservation of angular momentum does not allow torque 'out of nothing'.
He also says net force is zero, meaning the sum of the force vectors is zero.  The force vectors are obviously not the torque vectors, since (the part you never remember) force is not torque.

We can see, that if the torque is not there then there is no precession, minute 48.
The wheel is stable, no net force without the additional weight on the axle.
Also the wheel is stable no net force with the additional weight on the axle with the precession.

No, there is still no net force, as evidenced by the fact that the setup doesn't go up, down, left, right, or whatever.  f=ma, so absent any linear acceleration, there can be no net force acting on the wheel. 

What are the causes of the precession effect?

If it is precessing, then there must be a net torque on it, which necessarily changes (accelerates) the angular velocity vector ω.

The external torque on the angular momentum of a rotating wheel.

The torque does it.  It is not 'external' torque, since that word conveys no additional meaning.  Angular momentum does not cause precession, as evidenced by the lack of precession when no torque is applied.

Both are required, if one is missing then there is no precession.

Reasonable statement.  If angular momentum was zero, there would be no ω vector to precess. Torque would still cause the exact same angular acceleration, but it wouldn't be considered precession in that scenario.

[Jaaanosik (OP)]

I didn't respond to several posts due to obvious lack of reading prior responses.
You're still assuming that force is torque, which is going to give you wrong answers every time.

Professor Lewin says: "There is no net force on that wheel, but there is a net torque."
What is a net torque? Out of nothing?

Net torque means that the sum of the torque vectors acting on the wheel is nonzero.  No, those torques must be transferred to the wheel.  Conservation of angular momentum does not allow torque 'out of nothing'.
He also says net force is zero, meaning the sum of the force vectors is zero.  The force vectors are obviously not the torque vectors, since (the part you never remember) force is not torque.
...

Halc,
If an object is not moving, it is stationary, then it does not have a kinetic energy.
The kinetic energy comes from a force in mechanical systems.
Minute 48 of the video, the weight and the axle have NO kinetic energy.
When professor releases the weight from his hand the weight and the axle start to rotate, they have the rotational kinetic energy.
Where did the rotational kinetic energy come from?
Jano

[Halc]

The kinetic energy comes from a force in mechanical systems.

Forces are involved to change kinetic energy, but net forces are not necessarily involved.  Torque is not force, and yet X torque applied for time T to a system can (doesn't necessarily) result in some amount of kinetic energy change to the system regardless of the magnitude of the forces used to achive said X torque.
Anyway, in context of your post here, I know what you mean.

When professor releases the weight from his hand the weight and the axle start to rotate, they have the rotational kinetic energy.
Where did the rotational kinetic energy come from?

The precessing disk applied a momentary torque (not any net force) to the axle.  No continued torque is required once the axle gets its steady state angular momentum (a small vector pointing down)

[Jaaanosik (OP)]

The kinetic energy comes from a force in mechanical systems.

Forces are involved to change kinetic energy, but net forces are not necessarily involved.  Torque is not force, and yet X torque applied for time T to a system can (doesn't necessarily) result in some amount of kinetic energy change to the system regardless of the magnitude of the forces used to achive said X torque.
Anyway, in context of your post here, I know what you mean.

When professor releases the weight from his hand the weight and the axle start to rotate, they have the rotational kinetic energy.
Where did the rotational kinetic energy come from?

The precessing disk applied a momentary torque (not any net force) to the axle.  No continued torque is required once the axle gets its steady state angular momentum (a small vector pointing down)

Halc,
There is only rotating disk/wheel in the beginning.
Professor even says that the rotating wheel is suspended in such a way that there is no gravitational torque on it, 47:14 min.
The rotating disk cannot provide/cause a torque. It is steady by itself, just a constant angular velocity.
It does not have units of measure for it, does it?
You are right, small vector pointing down.
There had to be I*a (rotational inertia * angular acceleration); what is the cause?
The only cause is a net force. An object cannot start rotating without a net force.
A torque is a net force (90 degrees component) applied at a distance from the axis of rotation, Nm units of measure.

The w_precession = T/L  torque over the rotational inertia of the wheel.
If one of them is missing then there is no precession.
Both have to be present.
Therefore: "The precessing disk applied a momentary torque (not any net force) to the axle.  No continued torque is required once the axle gets its steady state angular momentum (a small vector pointing down)"
is wrong. It is not a momentary torque. It is a constant torque.
You can attach the weight to the rotating wheel axle on the ISS and it is not going to precess,
Jano

[Halc]

There is only rotating disk/wheel in the beginning.
Professor even says that the rotating wheel is suspended in such a way that there is no gravitational torque on it, 47:14 min.

Which means that at no time does the weight of the disk contribute to the torque acting on the disk, quite unline the other video with the guy supporting the thing well away from its center of gravity.
There's no way to work out the weight of the spinning disk from what he's doing, even knowing the weight of the objects he adds, and the distances, etc.

The rotating disk cannot provide/cause a torque.

It can, but while undisturbed, it doesn't.  This is no different than saying a mass in space cannot provide/cause a force, but if a force X is applied to said mass with my hand, the mass will provide a equal an opposite force -X to my hand, all per Newton's laws of motion. Likewise, the rotating disk is capable of exerting opposite torque to any object exerting torque on the disk.

It is steady by itself, just a constant angular velocity.
It does not have units of measure for it, does it?

Angular velocity is measured typically in radians/sec. The disk has quite a bit of angular velocity.  The axle has none before the precession starts.

You are right, small vector pointing down.
There had to be I*a (rotational inertia * angular acceleration); what is the cause?
The only cause is a net force.

Wrong again. Force is not torque. You are incapable of learning this.
There is no net force on the axle ever, as evidenced by the fact that its center of gravity never moves.

An object cannot start rotating without a net force.

Same mistake, again and again. Sad really.

The w_precession = T/L  torque over the rotational inertia of the wheel.

That's wrong as well, but at least you're using torque now instead of force. L is angular momentum, not rotational inertia.

Therefore: "The precessing disk applied a momentary torque (not any net force) to the axle.  No continued torque is required once the axle gets its steady state angular momentum (a small vector pointing down)"
is wrong. It is not a momentary torque. It is a constant torque.

The angular velocity of the axle is constant, changing only when the weight is added or removed. That means the torque is momentary. No additional torque is needed to rotate something that's already rotating. Instead of asserting all these things, why don't you consider the implications of your assertions, which run into contradictions.  If there is continuous torque on the axle, why does its angular velocity not change after that moment when the weight is added. That's would be a contradiction.

You can attach the weight to the rotating wheel axle on the ISS and it is not going to precess

There is no weight on the ISS.

Please reply with some intelligent thought put into your remarks. I see little point in responding to what are obviously either troll assertions or massive ignorance. Retake your middle-school physics classes, or at least get a refund from your education system that so grossly failed you.

[Jaaanosik (OP)]

...]The angular velocity of the axle is constant, changing only when the weight is added or removed. That means the torque is momentary. No additional torque is needed to rotate something that's already rotating. Instead of asserting all these things, why don't you consider the implications of your assertions, which run into contradictions.  If there is continuous torque on the axle, why does its angular velocity not change after that moment when the weight is added. That's would be a contradiction.

You can attach the weight to the rotating wheel axle on the ISS and it is not going to precess

There is no weight on the ISS.

...

Halc,
this is our major disagreement.
The wheel axle rotation, the precession, is not going to happen if there is no torque from the weight.
The torque and the angular momentum have to be present to cause the precession.
The precession, the rotation, is not going to happen when the weight is taken away of the axle.
The torque has to be constant, continuous.
Yes, I should have said mass of the brass cylinder weight added to the axle of the rotating wheel on the ISS.
I had this physical weight object in mind when I said that, not weight as a force.
This is the proof that the precession does not happen when there is no torque but there is an angular momentum of the wheel,
Jano

[Jaaanosik (OP)]

...]The angular velocity of the axle is constant, changing only when the weight is added or removed. That means the torque is momentary. No additional torque is needed to rotate something that's already rotating. Instead of asserting all these things, why don't you consider the implications of your assertions, which run into contradictions.  If there is continuous torque on the axle, why does its angular velocity not change after that moment when the weight is added. That's would be a contradiction.

You can attach the weight to the rotating wheel axle on the ISS and it is not going to precess

There is no weight on the ISS.

...

Halc,
Why a boat does not continue moving at a constant velocity on water once it is moving and boat engines are turned off?
The rotational inertia of the wheel does not want to rotate in the precession motion by itself.
The rotational inertia resists the precession, it is being forced into the precession by the torque,
Jano

[Jaaanosik (OP)]

...]The angular velocity of the axle is constant, changing only when the weight is added or removed. That means the torque is momentary. No additional torque is needed to rotate something that's already rotating. Instead of asserting all these things, why don't you consider the implications of your assertions, which run into contradictions.  If there is continuous torque on the axle, why does its angular velocity not change after that moment when the weight is added. That's would be a contradiction.

You can attach the weight to the rotating wheel axle on the ISS and it is not going to precess

There is no weight on the ISS.

...

Halc,
The bold statement is true for a rigid body, a mass, ...
The bold statement is not true for the rotational inertia.

This is very similar to the following scenarios:
- holding a weight in a stretched hand, no potential energy change for the weight but it costs energy to hold the weight.
- an astronaut going in a circle around the ISS with the jets on his back costs energy though the kinetic energy does not change for the astronaut in the ISS frame.

- hanging the weight on a string, no potential energy change for the weight and it does not cost any energy.
- the astronaut going in a circle around the ISS attached with a string, no kinetic energy change and it does not cost any energy.
... the same results as the above but no energy cost.

The torque rotating the angular momentum is doing work even though it appears there is no potential energy change.
Jano