You multiply the force (F) that is perpendicular to "d", right?
Not parallel?
Not parallel?
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If a force is directed exactly toward or exactly away from the point about which you calculate the moment of it, then there is ZERO moment of that force.
There only exists a moment of a force, if the force is directed in a manner whereby which it COULD cause some rotation, should the object be fixed at a pivot for the point about which you calculate moments. This can only happen, if the force has a line of action that is offset from the point about which you take moments.
It is that offset distance d, that is what you use when calculating moment of a force. That offset distance d, is the ABSOLUTE minimum distance between the line of action, and the point about which you calculate moments. Indeed, if drawn, you will see that the distance d is perpendicular to the force's line of action.
And as an alternative method, you can take a cross product. r cross F. The radial coordinate of ANY point on the force's line of action cross product with the force, both as vectors. This calculates moment of the force, as well. You see the sine term in the cross product function, this is what extracts only the perpendicular component of the radius vector, in calculating the moment.
Another word for moment is torque. Physics likes the word torque, engineering likes the word moment. Actually, engineering uses both the words torque and moment, and has a geometric distinction between them. In engineering, a torque is directed along the member's long direction, like torsion of a shaft. And a moment is loading the member perpendicular to its long direction, like bending of a beam.
Physically, it is all the same stuff, whether it be torque or moment. It is just a bookkeeping thing, why engineering likes using both terms.
There only exists a moment of a force, if the force is directed in a manner whereby which it COULD cause some rotation, should the object be fixed at a pivot for the point about which you calculate moments. This can only happen, if the force has a line of action that is offset from the point about which you take moments.
It is that offset distance d, that is what you use when calculating moment of a force. That offset distance d, is the ABSOLUTE minimum distance between the line of action, and the point about which you calculate moments. Indeed, if drawn, you will see that the distance d is perpendicular to the force's line of action.
And as an alternative method, you can take a cross product. r cross F. The radial coordinate of ANY point on the force's line of action cross product with the force, both as vectors. This calculates moment of the force, as well. You see the sine term in the cross product function, this is what extracts only the perpendicular component of the radius vector, in calculating the moment.
Another word for moment is torque. Physics likes the word torque, engineering likes the word moment. Actually, engineering uses both the words torque and moment, and has a geometric distinction between them. In engineering, a torque is directed along the member's long direction, like torsion of a shaft. And a moment is loading the member perpendicular to its long direction, like bending of a beam.
Physically, it is all the same stuff, whether it be torque or moment. It is just a bookkeeping thing, why engineering likes using both terms.
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yes you multiply force with the perpendicular distance to pivot ( that means that the distance "d" must be perpendicular to direction of force "F") and the unit for moment is N.m not Joules