Statics : Direction of Moments

[Gian Lukmana]

I still don't really get the concept of moments..

if moment is what makes things rotate, imagine this :

....... F (pushing down the stick)
===================(stick)
A

so :
1. the stick will rotate in a clockwise direction,
2. but the direction of the moment is negative Z.. (right hand rule)
I just don't get the correlation between the two !
my mind : The stick will rotate in a clockwise direction, and has nothing to do with the Z axis..

Anyone.. ?

 

[A.T.]

The stick will rotate in a clockwise direction, and has nothing to do with the Z axis..

Which way does the angular velocity vector point, when it rotates in a clockwise direction?

 

[Chandra Prayaga]

I still don't really get the concept of moments..

if moment is what makes things rotate, imagine this :

....... F (pushing down the stick)
===================(stick)
A

so :
1. the stick will rotate in a clockwise direction,
2. but the direction of the moment is negative Z.. (right hand rule)
I just don't get the correlation between the two !
my mind : The stick will rotate in a clockwise direction, and has nothing to do with the Z axis..

Anyone.. ?

It depends on how you choose your coordinate system. If you choose the x-axis along the stick, and the y-axis vertically up on the page, then the z axis is out of the page for a right handed coordinate system. Once you fix your axes like that, a clockwise moment is described by a vector which points in the negative z direction.