Question

write the expression for the moment of force about a given axis

Answer 1

The moment of a force  about an axis p is defined as the projection OB on p of the moment. Moment of the force F about the axis p.

Denoting  the unit vector of p, the moment Mp of force  about an axis p can be expressed as scalar product (dot product)

Mp =  . (3.22)

or as the mixed triple product of the unit vector , the position vector , and the force :

Mp =  . (×)(3.23)

Using the determinant form for the mixed triple product, we have the magnitude of the moment

Mp = (3.24)

where,,are direction cosines of axis p x, y, zare components of  Fx, Fy, Fzare components of