- #1
Trickster_00
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In summary, The force in an equation of ∑ri x Fi ≠ 0 can act through any point, not just the origin. This is because a couple can be replaced by two equal and opposite forces in the same plane, which can be adjusted in magnitude and direction to cancel out the given force, leaving only the other force in the couple.
- #2
tiny-tim
Science Advisor
Homework Helper
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Hi Trickster_00! 
it can act through anywhere
you could write it as a force acting through (97,6,300000) if you wanted to, but the accompanying couple would be different
(btw, if the force and the couple were co-planar, you could choose to make the couple vanish)
Trickster_00 said:
it can act through anywhere
you could write it as a force acting through (97,6,300000) if you wanted to, but the accompanying couple would be different
(btw, if the force and the couple were co-planar, you could choose to make the couple vanish)
- #3
tiny-tim
Science Advisor
Homework Helper
- 25,839
- 258
oh, I see you've asked about that in another thread …
it's because we can always replace a couple by two equal and opposite forces in the same plane as the couple …
so we can make the two forces any magnitude we like, and in any direction in that plane that we like, so long as we adjust the distance between the two forces …
so make one of the two forces (in the couple) equal and opposite to the given force …
Trickster_00 said:
it's because we can always replace a couple by two equal and opposite forces in the same plane as the couple …
so we can make the two forces any magnitude we like, and in any direction in that plane that we like, so long as we adjust the distance between the two forces …
so make one of the two forces (in the couple) equal and opposite to the given force …
then they cancel, leaving only the other force in the couple
FAQ: Question about System of Forces
What is a system of forces?
A system of forces refers to a group of forces acting on an object or system. These forces can be either external or internal and can affect the motion or equilibrium of the object.
How do you determine the resultant force in a system?
The resultant force in a system can be determined by adding all the individual forces in the system together using vector addition. This will give the magnitude and direction of the resultant force.
What is the difference between a concurrent and a non-concurrent system of forces?
A concurrent system of forces is one where all the forces act through a common point, while a non-concurrent system has forces acting at different points. In a concurrent system, the resultant force can be found by simply adding all forces together, while in a non-concurrent system, vector addition must be used.
How do you calculate the moment of a force in a system?
The moment of a force is calculated by multiplying the magnitude of the force by the perpendicular distance from the point of rotation to the line of action of the force. This can be represented mathematically as M = F x d.
Can a system of forces be in equilibrium even if there are multiple forces acting on it?
Yes, a system of forces can be in equilibrium even if there are multiple forces acting on it. This means that the forces are balanced and the object is either at rest or moving with constant velocity. In order for a system to be in equilibrium, the sum of all forces must be equal to 0 and the sum of all moments must also be equal to 0.