- #1

- 139

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ho do i express the moment in terms of vectors like 3i+4j etc.

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- Thread starter chandran
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- #1

- 139

- 1

ho do i express the moment in terms of vectors like 3i+4j etc.

- #2

- 26

- 0

- #3

- 139

- 1

that is ok. what i need is the moment vector in the form of ai+bj+ck. In this problem the moment vector is 0i+0j+3k. Is it correct?

But on seeing a moment vector like this ai+bj+ck how can one know at which point the moment vector is acting? In this problem

the moment vector is acting at a point at the right end of the beam which is SAY a distance L from the left end of the beam(i.e the orgin of

the vector's coordinate system). But this vector ai+bj+ck alone is not able to give the position. Why

- #4

- 26

- 0

Your answer is still incorrect because of the direction in the k direction. Use your right hand rule again. Your thumb should be pointing into the paper. If that is the case then the moment is acting along the negative Z axis or negative k direction.

The moment has no components in the x or y directions therefore the magnitude in the i and j directions are 0.

Think of it this way. The magnitude of a moment is equal to

[tex]rFsin\theta[/tex] Where [tex]\theta[/tex] is the angle between the force creating the moment and the axis in which the moment is rotating around. Therefore the maximum moment is when the angle is 90 degrees a thus the sine of it equals 1. This also means that there is no component of the force or the moment in any other directions aside from the line of action. As a result your moment is only in one direction the negative z direction.

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