Difference between torque and moment

[Studiot]

Boosting your post with a copy of mine in no way enhances the paucity of your reply.

If you read my post properly you would have seen that I displayed one example that negates all your theory.

Let me ask you this one question.

Your 3 dimensional theory of moments has to work in all cases and situations, to be universally valid.
That means it has to work in the case where we are restricted to 2 dimensions.
If it is unable to accomplish this then it fails.

 

[realXenuis]

Boosting your post with a copy of mine in no way enhances the paucity of your reply.

Huh? I added content. I can't be blamed for your lack of reading comprehension, can I?

If you read my post properly you would have seen that I displayed one example that negates all your theory.

No, you drew a picture.

Let me ask you this one question.

Your 3 dimensional theory of moments has to work in all cases and situations, to be universally valid.

It's not my theory, it's Beer, Johnston, Mazurek, and Cornwell's, the writers of my Static's book. But i guess it's possible you know more than they do about it? Wait, no you don't, nevermind.

That means it has to work in the case where we are restricted to 2 dimensions.
If it is unable to accomplish this then it fails.

This makes no sense. You're just making up sentences now. Are the rest of your 1600 posts on the physicsforum of this high quality?

You really shouldn't reply. Why would you want to intentionally mislead people about Moments on a Physicsforum thread?

 

[Studiot]

Perhaps a little history might help?

Ca 250 BC
The mechanics of turning effects was known to the ancient world for example the principle of levers attributed to Archimedes.

1725
The term moment was introduced and formally defined by Varignon in his book
'Nouvelle Mechanique.'
“The moment of a force, P, about a point O is defined as the product of that force into the perpendicular OM drawn to its line of action from O, this perpendicular being reckoned positive or negative according as it lies to the left or right of the of the direction of P."

1750 – 1804

St Vennant investigated the torsion of prismatic bars and posed St Vennant’s Problem.
He did not however introduce new concepts in turning.

1804 -1806

Poinsot published his book 'Elements de Statique' and the theorem that bears his name.
This introduced two things. He defined and introduced the term ‘couple’ and the theorem which states that in 3 dimensions any system of forces may be reduced to a single force plus a couple, in a plane perpendicular to the line of action of the force.
He clearly defined his couple to exist in a plane.

1912
Lamb, one of the most prominent applied mathematicians of his time, proposed that the term ‘torque’ be introduced to replace ‘couple’

Lamb 'Statics' p52.

“Since a couple in a given plane is for the purposes of pure statics sufficiently defined by its moment, it has been proposed to introduce a name torque or twisting effect which shall be free from the irrelevant suggestion of two particular forces.”

This suggestion was not, however generally adopted.

Indeed the three most influential texts ( in this subject) of that era and since carried on as before.

1926 Love ‘A Treatise on the Mathematical Theory of Elasticity’

1936 Southwell ‘Theory of Elasticity’


These both refer to ‘Torsional Couples’ for the 3D effects described in St Vennant’s Problem.

1934
Timoshenko published the third standard text, ‘Theory of Elasticity’ and clearly establish torque in this 3D role.

In fact most authors in the second part of the 20th century have followed the notation set by Timoshenko in elasticity.

What I have said is in total accord with the established Timoshenko convention. It has suited most purposes well and I see no compelling reason to change it.

 

[realXenuis]

Perhaps a little history might help?

Perhaps it would. If this were a thread about the history of something. Or perhaps if it provided evidence of your claims. But it's not, and it doesn't.

The subjects of our disagreements aren't interpretive. You either understand them or you don't. You obviously don't. This is a physics forum, it's not a rhetoric forum. Continuing to redefine concepts like Moment is not constructive to learning or understanding. This is problematic on a forum that exists to help educate and elucidate on these subjects. Please stop propagating misinformation.

What I have said is in total accord with the established Timoshenko convention. It has suited most purposes well and I see no compelling reason to change it.

No, what you've said is:
1. A Moment doesn't require a position vector.
2. A Moment doesn't require 3 dimensions.
3. There is no distinction between a Moment and the magnitude of a Moment.
4. When a couple is applied, Torque or Moment is not necessary to cause a body rotation. It just magically rotates.
5. A Moment vector is not a real vector, as it does not exhibit the commutative property of addition
6. Every force has a moment about every single point in space.
7. Position vectors only add complication to the analysis of a Moment
8. To create a moment all you require is a point and one single force.
9. To create a couple in a plane, all that is needed is a second nonconcurrent force

I'm sure I could list more. This is probably enough.

I disagree with all of these points. I have provide, and can provide more, evidence to support my understanding of them. This evidence is not created by me, but found externally. I didn't draw a picture. I did need to create another example to demonstrate why I am correct.

You still refuse to provide evidence. You avoid answering simplified yes/no answers to simple questions that illustrate your understanding of these very specific concepts. I won't mention your numerous contradictions, incomplete, hand-drawn examples, and a comical attempt at history, which, hilariously, was itself provided w/no evidence.

I really hope your posts on other threads in the physics forums were more informed.

 

[D H]

This thread has degenerated into a sophomoric debate over terminology. Moreover, the terms being debated have slightly different means in physics and engineering, as well as from text to text.

Thread locked pending moderation.