How to Find the Torque About a New Point Using Vector Cross Products?

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Homework Help Overview

The discussion revolves around calculating torque using vector cross products, specifically focusing on how to find torque about a new point rather than the origin. The original poster describes a two-part problem involving position and force vectors, successfully solving the first part but struggling with the transition to the second part, which involves a different point of rotation.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster considers the implications of changing the point of rotation from the origin to a new point (a,b) and questions how to adjust the position vector accordingly. Some participants suggest using the new position vector relative to the new point while others discuss whether the force vector should also be adjusted.

Discussion Status

Participants are actively engaging with the problem, offering suggestions on how to redefine the position vector. There is a mix of interpretations regarding the treatment of the force vector in relation to the new position vector. Some guidance has been provided, but no consensus has been reached on the exact approach to take.

Contextual Notes

The original poster expresses uncertainty about the transition from the first part of the problem to the second, indicating a potential gap in understanding the underlying concepts of torque and vector relationships. There is also a note of a participant emphasizing the importance of theoretical understanding before attempting problem-solving.

Impathy
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I have a two-part problem. The first part gve me a position vector r and a Force vector F acting upon r and I needed to find the magnitude of the torque about the origin. I took rxF and got the correct answer. Part two asks me to find the torque about the a new point (a,b). So instead of r rotating about the origin, it is now rotating about (a,b)? I was okay with the first part, but I just don't understand what's going on with the second part and how to attempt it. I was thinking of a few things regarding the distance between the origin and (a,b) and crossing that with F ... I just don't know what to do ... help! :D Thanks in advance, you guys are always terrific!
 
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If the position vector (the position relative to the origin) is <x,y>, then the position relative to point (a,b) is the vector <x-a, y-b>. Use that instead of vector r.
 
Alright ... do I just do that to the position vector, or do I do it to the force vector as well and then cross product the new position and new force? Or do I just use the new position and the old force?
 
Actually, it would make sense to use the "new" position and the "old" force, I suppose, right?
 
While finding force you have a force vector, then the vector r, is the position vector drawn to the point at which the force vector is acting on the body with respect to a given point about which the object is rotating. since the point of rotation has changed, the position vector has changed. you must know to give the position vector in notations once the tail and the head points are given.
If you know this fact your doubt is meaningless and if you don't know, you are not good enough to do a torque problem. please read theory parts given in your book before starting to solve a problem. that will be more a healthier habit.
 

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