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dE_logics
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Torque is when a couple is formed...and for a moment, a couple needs not be there right?
You topple if you get down from a rapidly moving bus because of the torque exerted by friction alone..Torque is when a couple is formed...and for a moment, a couple needs not be there right?
tiny-tim said:Torque is the moment of a force about a point.
dE_logics said:… confusing.
Balanced or unbalanced, moment of a force about a point is called torque. All you need is a force and a reference point. A force doesn't cease to exist just because it is neutralized by some other force.dE_logics said:You mean in case the moment by each force is not balanced, then it will make a torque.
sganesh88 said:Balanced or unbalanced, moment of a force about a point is called torque. All you need is a force and a reference point. A force doesn't cease to exist just because it is neutralized by some other force.
so I thought I'd at least clear this one up.
Studiot said:There are two real differences between a moment (or couple) and torque.
Firstly Torque is not limited to a single revolution.
Secondly moments (and couple) are planar beasts - they exist in a plane. Torque, on the other hand, is three dimensional and has the ability to transfer moments from one plane to another.
Moments/couples certainly exist in 3-D. Their resultant vector projects into the third dimension. This is no different than a Torque.
Couples transfer moments the same as Torques, being free vectors.
Is a Moment limited to a single revolution? Please, show me where or how.
Studiot said:Perhaps you can display a non planar couple?
See your remark below:
If the two forces constituting the couple are not in the same plane how can there be a zero force resultant?
The Couple is in 3-D. The Forces that create the couple are planar. The two (or more) Forces are just forces, they are not a Couple. They create a Couple, which HAS to include the resultant vector, perpendicular to the two Forces from which it was created. If you have a "thing" with 3 vectors (or more), and at least one of those vectors is not coplanar, it fills 3space. If you're constraining a Couple to 2space, then it's resultant is a magnitude (and thus, Cross Product will not work, etc etc.).
A single force (line) and a single fulcrum (point in space)can only be planar.
And moments certainly do not need three dimensions.
Yes, they do. Moments NEED 3 dimensions. It is in the example I've give you. Show me yours.
If you take the case of the root an encastre cantilever, there are two support reactions.
One of these is a moment, not a force, nor yet a couple. In other cases a bending moment may be the result of a couple.
Show me an example, online.
If you introuduce a second non concurrent force to the system you can create a couple.
No, you MUST introduce a second force to create a couple, but that's not enough, the force also has to have equal magnitude, opposite direction, and not reside along the line of action of the first force. Just having another force be concurrent is not enough, actually.
If we have a shaft and apply a single couple to it we simply have a rotating shaft. No torque is involved.
No, we have a shaft and a couple. Rotation is not necessary, we still have a torque and a moment. We have a body, acted upon by forces in the configuration of a Couple. Because it happens to be rotating changes nothing. There is mass, and it's being acted upon by rotational (as opposed to translational) forces. There IS torque/moment. And it DOES include a position vector. These are the kind of posts that add to the confusion. This is why I posted in the first place.
I think you're probably trying to use specifically an example of a FRICTIONLESS SHAFT. Ignoring that there is no such thing in reality, still, you are rotating a body when you apply a couple. When analyzing the system, the shaft would be included in any free body diagram. If that body has mass, then you have Torque (couple). There is no getting around that. If there is no body (mass) then you have nothing to apply force to. This is a simple concept, and building up complication does not make your argument work any better. In fact, you made my argument for me: a couple applied to a shaft made the shaft rotate. It had to have torque/moment. You would agree now, right?
You've misunderstood. I simply asked for an example. I don't believe I mentioned my knowledge of the subject. If it were true that I did NOT know how an encastre cantilever works, would this change the arguments you've given? It doesn't have to veer down the path of "I know more than you". THAT would be a p___ing contest. Now, if you link to an example, we can go from there, no?
No, you MUST introduce a second force to create a couple, but that's not enough, the force also has to have equal magnitude, opposite direction, and not reside along the line of action of the first force. Just having another force be concurrent is not enough, actually.
Studiot said:Here is a simple plane frame, with three identical cantilevers, loaded with weights, W.
I have chosen to place the origin at the bottom left hand corner, so all position vectors are measured from here, by definition.
I have shown the support reactions for each cantilever (of course they are all equal).
However since the cantilevers are located in different places the postion vectors to their respective roots, A, B and C are different.
I repeat, despite different position vectors their support reaction moments are identical.
Why do I need three dimensions to analyse this frame? All the necessary analysis is independant of the third, z, axis.
I never said you need 3 dimensions to analyze a frame. I said a Moment requires 3 dimensions to be a Moment. You can very well call that a position vector and that a force vector, and then talk about Moments, but what you're really talking about is the magnitude of a Moment. Once you cross these vectors to find an ACTUAL Moment, you get a third dimension. A true Moment is not required to analyze this plane. Only the magnitude. You have not demonstrated a moment. Which, once again, brings us back to your misunderstanding of what a Moment is.
What benefit do I derive from employing position vectors in the analysis?
It is true that for instance the method of tension coefficients (which does use position vectors) might be employed.
It's not a benefit. It's a necessity, if you're talking about actual Moments. If you are analyzing Moments in 2-d, you're doing so for simplicity, and you're getting magnitudes of Moments. Just as, by showing the forces to be parallel to x/y axes, you're gaining simplicity in the analysis. But you should understand, that's not a moment until that Moment vector is projected into the z plane. In your example, you're talking about a scalar quantity of moment. A magnitude. Not a vector quantity. It's convenient to use 2-d for analysis. But remember, real cantilevers in real life occupy real (3-d) space.
I'll respond to the rest of this when i get home. Will you answer the questions I've asked? Will you provide evidence of your understanding that a Moment doesn't require 3 dimensions and a position vector? My guess is you will ignore these once again. You're not getting anywhere, Studiot, and you're continuing to propogate misinformation by refusing to back up your incorrect understanding of what a moment requires, and the rest of the issues I've elucidated. Do you disagree? The prove it.
Your other claim is that torque and moment and couples are identical.
Please describe the two forces required to create a couple acting at A, B and C
If a moment or couple were applied to a cantilever in a plane parallel to the yz plane this would produce a torque on the cantilever about the x axis. This effect of this torque would be felt all along the cantilever, not just in the plane where it is applied.
Would the support reaction moments have any such effect anywhere else on the z axis, other than in the plane of the frame? Obviously not.
I think that covers all your beefs.
Studiot said: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.
Studiot said: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.
Torque and moment are two terms used to describe the rotational force applied to an object. Torque is the measure of the force that causes an object to rotate around an axis, while moment is the measure of the tendency of an object to rotate around a fixed point.
Torque and moment are closely related as they both involve rotational forces. Torque is the actual force applied to an object, while moment is the measure of the effect of that force on the object's rotation.
Yes, torque is typically measured in units of force multiplied by distance, such as newton-meters or pound-feet. Moment, on the other hand, is measured in units of force multiplied by distance squared, such as newton-meters squared or pound-feet squared.
Torque and moment are important concepts in engineering and physics, and have many practical applications. They are used in the design and analysis of machines and structures, such as engines, motors, and bridges. They are also important in understanding the forces involved in sports, such as golf swings and baseball pitches.
To calculate torque, you must know the force applied and the distance from the point of rotation. The formula for torque is torque = force x distance. Moment can be calculated by multiplying the torque by the distance from the point of rotation to the point where the force is applied.