[alancalverd]

 

They receive the exact same question and options as the poll of this thread.

Precisely my point. If you ask any parasitical consultant "can we improve the safety of a motor car" he will scour the internet for a hundred ways in which you might do so, but won't answer "it's good enough for competent drivers". So you end up with all the EU-mandated stuff like lane-keeping and speed limit sign recognition that makes driving actually dangerous and distracting.

Similar result here. We have a quantity, force x distance, that is absolutely consistent and completely understood by those who use it every day, but because it can be used in the magical context of rotation various ignorant people think it ought to involve some measure of angle. Problem is that if you incorporate angle as you propose, it gives you absurd numbers when θ → 0.

[hamdani yusuf (OP)]

They receive the exact same question and options as the poll of this thread.

Precisely my point. If you ask any parasitical consultant "can we improve the safety of a motor car" he will scour the internet for a hundred ways in which you might do so, but won't answer "it's good enough for competent drivers". So you end up with all the EU-mandated stuff like lane-keeping and speed limit sign recognition that makes driving actually dangerous and distracting.

Similar result here. We have a quantity, force x distance, that is absolutely consistent and completely understood by those who use it every day, but because it can be used in the magical context of rotation various ignorant people think it ought to involve some measure of angle. Problem is that if you incorporate angle as you propose, it gives you absurd numbers when θ → 0.

You seem to have forgotten about the definition of derivative.

https://en.m.wikipedia.org/wiki/Derivative


Maybe that's why you failed to understand torque as the rate of change of angular momentum.

[hamdani yusuf (OP)]

You have not answered the question, you are trying to avoid it by digressing. Will the fly be crushed?

If the elevator is free falling, no. Otherwise, it depends on the acceleration and the strength of the fly.

[hamdani yusuf (OP)]

Indeed, Alan, I have noticed this too. They rarely if ever disagree with the questioner and frame answers in a way to largely accept the question regardless of how absurd it may be.

Can you try to convince them to choose option#1?

[hamdani yusuf (OP)]

In its answer, Qwen3 rephrased the options from my original poll, and then evaluated each option before finally make a conclusion. What do you think is wrong with its reasoning? What should be changed to make its reasoning correct?

Qwen 3 235B answers.

>
> Looking at the options given in the problem, the user is asking which conclusion is best. The options are:
>
> 1. Current units are perfect.
> 2. Problems exist but no solution.
> 3. Problems exist and there are possible solutions.
> 4. There's a single comprehensive solution.
>
...

### Evaluation of Options:
1. **Option 1 ("Current units are perfect")**: This is demonstrably incorrect, as the issues outlined above are widely recognized in physics and engineering communities. The dimensionless nature of radians and unit overlap are active topics of discussion.

2. **Option 2 ("Problems exist but no solution exists")**: This is overly pessimistic. Numerous proposals (e.g., explicit radians in units, formalizing radians as a base unit) exist to address these challenges, indicating that solutions are both possible and actively pursued.

3. **Option 3 ("Problems exist and there are possible solutions")**: This aligns with the evidence. The ongoing discussions and proposed modifications to unit conventions reflect a recognition of the issues and a commitment to addressing them. For example, the use of radians in torque units (N?m/rad) is already practiced in some contexts to avoid confusion with energy.

4. **Option 4 ("Single comprehensive solution exists")**: This is overly optimistic. While specific solutions (e.g., explicit radians) address particular issues, there is no universally accepted, comprehensive overhaul of rotational units that resolves all challenges. The complexity of physical quantities and their interrelationships makes a single solution unlikely.

### Conclusion:
The most reasonable conclusion is **Option 3**: *The standard units have known problems and there are possible solutions*. This acknowledges the recognized issues (e.g., dimensionless radians, unit overlap) while recognizing the ongoing efforts to refine and improve the measurement of rotational quantities. Proposals such as explicit radians in units and formalizing radians as a base unit represent viable steps toward a more coherent system, even if a single, universal solution remains elusive.

**Final Answer:** 3

I think its thoughts are reasonable for most people who read them. At least no one have shown otherwise.

[Bored chemist]

The feedback system can only react to the change of torque AFTER the needle change its position, not before. Thus the torque measurement requires a change in rotational angle, no matter how small it is.

And the measurement of torque only happens after the system has moved the needle back to where it was (or, if you want, slightly higher).
Until then there is no measurement.

As I said, it is you who does not understand it

[paul cotter]

More absolute nonsense and digressions to avoid answering the question. I am asking about your example of the girl on the scales- will a fly under one of her feet get crushed, yes or no. If the fly gets crushed, which no one with the absolute minimum of common sense can dispute, then the force of the girl's weight has not been cancelled. Acceleration does not have any relevance with static forces. And you don't need to lecture us on differential calculus, all who are responding know the subject intimately.

[alancalverd]

Maybe that's why you failed to understand torque as the rate of change of angular momentum.

Probably because it isn't.
Torque is defined as the moment of a force around a point or axis. If is is applied to a body that is FREE TO MOVE, then that body will experience a change of angular momentum proportional to the applied torque. In practice, only bodies floating in space  actually meet that criterion, which is why we define torque as a cause, not an effect.

[Bored chemist]

And you don't need to lecture us on differential calculus, all who are responding know the subject intimately.

The big problem is that the OP suffers from delusions of adequacy.

[alancalverd]

and does not appreciate that Lim_(x→0)(1/x)  = ∞

[paul cotter]

Dunning Kruger comes to mind.

[hamdani yusuf (OP)]

The feedback system can only react to the change of torque AFTER the needle change its position, not before. Thus the torque measurement requires a change in rotational angle, no matter how small it is.

And the measurement of torque only happens after the system has moved the needle back to where it was (or, if you want, slightly higher).
Until then there is no measurement.

As I said, it is you who does not understand it

Not necessarily. A passive measurement system like Cavendish's torsion balance, the needle doesn't have to move back to where it was. What you said is not necessarily true. Some of your previous posts clearly show your confusions.

[hamdani yusuf (OP)]

Maybe that's why you failed to understand torque as the rate of change of angular momentum.

Probably because it isn't.
Torque is defined as the moment of a force around a point or axis. If is is applied to a body that is FREE TO MOVE, then that body will experience a change of angular momentum proportional to the applied torque. In practice, only bodies floating in space  actually meet that criterion, which is why we define torque as a cause, not an effect.

No. It's not the definition of torque. That's the source of your confusions.
You may deliberately forget or refuse to read my previous posts. But I'll just remind you, as well as other readers so they can learn from your mistakes.

Torque can be viewed as tangential force.

but not by anyone who can read the definition of torque.

Which one of these definitions?
a twisting force that tends to cause rotation. (oxford dictionary)

In physics and mechanics, torque is the rotational analogue of linear force. (wikipedia)

Alan said that torque is defined as perpendicular force times radius of rotation.
This is NOT a definition. it's just one of many equations relating torque to other physical quantities.
Some other equations related to torque are:
τ = I.α   = rotational inertia times angular acceleration
τ = dL/dt  = rate of change of angular momentum
τ = W/θ  = work divided by angular displacement
τ = P/ω  = power divided by angular velocity
They are all equally valid relationships. The fact that current standard units of rotational quantities are not always consistent with their involved equations tells us that at least one mistake must have been made in setting the standard.

Perpendicular force times radius of rotation is not the definition of torque. It's just an equation to calculate torque when the perpendicular force and radius of rotation is known. In other cases where they are unknown, we need to use other equations like mentioned above.

For example, a centrifugal pump running at 1500 RPM with 1000 Watt of power. The angular velocity and power consumption can be measured using a tachometer and a power meter. Motor efficiency can be calculated after comparing the power consumption when it's running decoupled and coupled to the pump.
The force by impeller exerted to the liquid is distributed across its surface. The complexity of the impeller shape and pump casing as well as the complexity of fluid dynamics make it hard to calculate the force at every point on the surface of the impeller.
The equation τ = F x R is practically useless here. The equation τ = P/ω  is more applicable in this case.

[alancalverd]

The equation τ = P/ω  is more applicable in this case.

Because it is explicitly derived from τ= F.r.

[Bored chemist]

A passive measurement system like Cavendish's torsion balance, the needle doesn't have to move back to where it was. What you said is not necessarily true. Some of your previous posts clearly show your confusions.

" A passive measurement system like Cavendish's torsion balance"
We are not talking about that.
You can tell from the video.

"the needle doesn't have to move back to where it was."
Nobody said it did; in fact I said it might not.
" What you said is not necessarily true."

What part of what I said  (And which I said was necessarily true) is not necessarily true?

[paul cotter]

BC, he will not answer your question. He tries to divert the discourse when questioned after saying something he cannot back up. He has avoided my question, re the "cancellation" of force.

[Bored chemist]

BC, he will not answer your question. He tries to divert the discourse when questioned after saying something he cannot back up. He has avoided my question, re the "cancellation" of force.

I know. And that's why I can't understand why the mods don't ban him.

[paul cotter]

Indeed BC, it is not a discussion but a diatribe.

[alancalverd]

I

can't understand why the mods don't ban him.

He's harmless, mostly confines his contributions to the "funnies", and does occasionally test the grey matter in trying to point out why he's wrong.  And I admire his enthusiasm and willingness to experiment.

[paul cotter]

I don't see him as quite harmless, he is the source of so much error that a third party could easily be misled. He does not debate, he just states his erroneous views and then doubles down on them, refusing to answer pertinent questions or tries to divert the discussion. Infuriating. I suggested previously that all his material be put in one thread and designated "an essay in confusion, too long to read".