Equivalent force-couple system (conceptual)

[jaredmt]

on a 3d graph i have 3 forces in different places pointing different directions. I am supposed to find the equivalent force-couple system about some point D. but 1 of the forces is aligned with point D and therefore creates no moment about D.

how would i do this? Do i just find the moment of all the forces about point D and then put the Resultant of the 3 forces on D?

 

[tiny-tim]

Hi jaredmt!

on a 3d graph i have 3 forces in different places pointing different directions. I am supposed to find the equivalent force-couple system about some point D. but 1 of the forces is aligned with point D and therefore creates no moment about D.

how would i do this? Do i just find the moment of all the forces about point D and then put the Resultant of the 3 forces on D?

Yup … add all the forces, and add all the moments …

if one of them is zero, that saves you time … so have a cup of tea!

 

[thomate1]

Yes, you are correct. In order to find the equivalent force-couple system about point D, you would first need to calculate the moment of all three forces about point D. This would give you the total moment of the forces acting on the point.

Next, you would need to find the resultant force of the three forces. This can be done by adding the three forces vectorially.

Finally, you would need to place the resultant force at point D, as it does not create any moment about that point. This would create an equivalent force-couple system at point D, with the same effect as the three original forces.

It is important to note that the resultant force should be placed at point D in such a way that it is perpendicular to the line connecting point D and the original force. This ensures that the moment of the resultant force is equal to the moment of the original forces.

I hope this helps. Let me know if you have any further questions.