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If there are multiple forces acting on an object at different locations on the object with different directions, how would you be able to find the origin and direction of the net force?

Qmechanic
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4 Answers4

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I assume that by origin of the net force you mean the point where the net force is applied.

You can choose whatever point of the body you like. Once you have chosen one point of the body, for each force acting on different points, you can add a pair of opposite forces, acting on the selected point, of the same modulus as the selected force. The force opposite to the original one will form with it a pure torque. All the members of the pairs with the same direction as the original applied forces will have the same application point and you may sum them according to the rules for vector sum.

The final result is that on the body there will be a net force acting on the selected point plus a net torque originating from the sum of all the torques. The construction is sketched in the following drawing: enter image description here

To the original force (arrow CE) acting on C, a pair of opposite forces acting on the selected point P have been added. The resulting system is a torque created by the forces (PE$_2$) and (C$_1$E$_1$) plus a force equal o (CE) But acting on P. As I stated above, any point can be used for this procedure, although in many cases it may be convenient to use the center of mass.

sammy gerbil
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GiorgioP-DoomsdayClockIsAt-90
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how would you be able to find the direction of the net force??

The direction is found by adding all the individual forces using vector addition

how would you be able to find the origin of the net force??

The origin of the force would be the origin of all the individual forces acting on the body

For example, You push a body to the right with a force $5N$ and another guy pushes it to the left with a force $2N$

The net force is $3N$ to the right. The origin of the net force is both the people who are individually applying the force.

Rishab
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  • "The origin of the force would be the origin of all the individual forces acting on the body" This is not clear, and unfortunately your answer doesn't shed light on it. – garyp Feb 17 '20 at 23:12
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You would need to define a coordinate system and then add the force vectors coordinates for the 2 or 3 perpendicular axes of your coordinate system. In a cartesian x,y coordinate system it would be helpful to put object centered on the origin and then find all the x and y components of force. To find the actual equations of motion you'll need to solve the torque equation as well.

enter image description here

Natsfan
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Direction is found by vector addition.And net force is always taken at COM.but net force is not used to find net torque you have to find net torque by adding torque by each force acting on it.

sarthak
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