Torque/Moment and Related Force Direction 1

[struclearner]

The direction of Torque/Moment is determined by Right Hand Rule, i.e, the thumb pointing in the direction when the fingers of Right Hand are curled in direction of rotation, and this is the Torque/Moment direction.
When there is a need to determine the direction of the Force by applying the torque, right hand rule will determine the direction of Force by the thumb pointing direction and this will be the direction of the force calculated/obtained from the Torque.
Thanks a lot for clarification.

 

[hydtools]

The thumb points in the direction of the moment vector. The fingers point in the direction of the force.

Ted

 

[TheTick]

Torque is a resultant of the cross product of force and displacement. If you want to determine a direction for an unseen force, you need to know at least the direction of the displacement.

 

[Jboggs]

"The thumb points in the direction of the moment vector. The fingers point in the direction of the force."
I might be wrong but my understanding of the Right Hand Rule is that it is simply a way to determine positive versus negative torque. The fingers show the positive direction and position relative to the axis of the force creating or resulting from the torque while the thumb shows the positive direction of the axis.

 

[rb1957]

is there a question being asked ?

most of the time I use the "right hand rule" visualisation to figure how to turn a nut.
And (sexist comment) when my wife tries it's "use your Right hand".

another day in paradise, or is paradise one day closer ?

 

[struclearner]

The refreshing/revisiting of the Right Hand Rule about the direction of Torque and Force comes in mind to find its application in understanding of the stretch/tensile force in a Bolt of a bolted joint, when it is being torqued.
As the bolt is torqued, it is stretched and the members of the bolted joint are compressed. Applying Right Hand Rule, if the fingers are considered curling in the direction of the rotation caused by the force, then the direction of the torque (pointing of the thumb)represents the direction of the force (axial/tensile force in the Bolt)?

 

[rb1957]

preload torque applies tension to the bolt … you don't need fingers or thumbs to know the direction of tension.

another day in paradise, or is paradise one day closer ?

 

[swimfar]

The right hand rule is just an arbitrary convention for which direction your moment vector points for a given applied moment. You could use a left-hand rule and you will end up with the same answer, as long as you are consistent. (But don't do that.)

 

[rb1957]

"arbitrary" in as much as 99.99% of threads are RH

another day in paradise, or is paradise one day closer ?

 

[drawoh]

struclearner,

I was not aware of a right[‑]hand rule for torque and moment. If you draw a diagram of a force and radius, the direction of the torque and moment is obvious.

Can you should us a picture of what you are trying to interpret?

--
JHG

 

[HTURKAK]

Torque/Moment is vectorial product of lever arm and force ; M = r X F

The direction of moment can be determined with right hand rule but inverse is not true..

 

[GregLocock]

If a rotation occurs about the z axis from the +x to +y direction then the rotation, torque and z axis are all positive in the direction of your thumb. Your curled fingers on the right hand indicate the motion of the rotation.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[struclearner]

As the bolt in a bolted joint is torqued, it is being stretched, the force of the torque acts along the axis of the bolt.
Does the Right Hand Rule of Torque/Force applies here, when the Torque is to tighten the joint, the force is tension.
When the torque is applied to untighten the joint, the force is in the opposite direction to relieve the tensile force obtained during the tightening of the joint.

 

[hydtools]

Yes, it applies. The thumb does not indicate the direction of the tensile force. The thumb indicates the moment(torque) vector direction. The fingers point in the direction of the applied force which creates the moment.

Ted

 

[rb1957]

I'm sorry but I don't understand the difficulty in the direction of tension.

The RH rule "thumb" does not show the direction of tension in the bolt. Yes, it shows the direction of the moment vector. In a practical sense it shows the direction of motion, the direction the nut moves when the torque is applied (along the fingers). Once the nut bears up against the plate the bolt stretches in the opposite direction to the thumb (as the nut tries to advance along the thread), and this is the preload tension. At the same time the joint plates compress together, this is the clamping that stops the plates from gapping.

another day in paradise, or is paradise one day closer ?