Direction of Torque: Understanding the Basics

[Amar.alchemy]

Hi,

Let us assume that I apply some amount of force at the end of the wrench to loosen a nut. This force makes the wrench to rotate in clockwise direction. So the direction of the torque should also be in clockwise direction.
However, we usually use the definition of cross product to determine the direction of Torque ie if both position vector and Force vector are in the xy plane then the direction of Torque will be either +ve z-axis or -ve axis depending upon the rotation of the body.
My confusion is why can't we say the direction of the torque is in clockwise direction or counter clockwise direction?? What exactly it means if we say the direction of the torque is along +ve z axis or -ve z axis??

 

[Doc Al]

My confusion is why can't we say the direction of the torque is in clockwise direction or counter clockwise direction??

For some purposes, it's perfectly OK to describe the torque as clockwise or counterclockwise. But what if you were looking at the wrench from the other side? Describing torque using an axial vector is more robust.

What exactly it means if we say the direction of the torque is along +ve z axis or -ve z axis??

Use the right hand rule to interpret the direction of the torque. If the torque is along the +ve z axis, that means that looking down (towards the -ve z direction) the torque would be counterclockwise.

See: http://hyperphysics.phy-astr.gsu.edu/HBASE/tord.html"

 

[Amar.alchemy]

For some purposes, it's perfectly OK to describe the torque as clockwise or counterclockwise. But what if you were looking at the wrench from the other side? Describing torque using an axial vector is more robust.

Use the right hand rule to interpret the direction of the torque. If the torque is along the +ve z axis, that means that looking down (towards the -ve z direction) the torque would be counterclockwise.

So when i say someone that the direction of torque is along the +ve z axis then it is necessary for him to know that torque is a cross product of positon vector and Force vector otherwise he can't tell whether it is clockwise or counter clockwise. Is my understanding correct??

And one more thing, in the thread I'm not able to view second paragragh of ur post, i saw it when i clicked "quote" button...

 

[Doc Al]

So when i say someone that the direction of torque is along the +ve z axis then it is necessary for him to know that torque is a cross product of positon vector and Force vector otherwise he can't tell whether it is clockwise or counter clockwise. Is my understanding correct??

No, all they have to know is the right hand rule convention for defining torque. (See the link in my last post.)

And one more thing, in the thread I'm not able to view second paragragh of ur post, i saw it when i clicked "quote" button...

That's probably because I was editing it while you were responding. You should be able to see it now.

 

[Amar.alchemy]

ya, Thanks i got it