|Imagine a seesaw, you apply 100 N
upwards on the left side of it, and on the right side, you apply 100 N down. Thus, Fy = 0, and since there's no horizontal force
acting upon it, Fx = 0. But it
This is because the forces are not acting on
the same line, not collinear.
But if 100 N was acting on both sides of the
seesaw and assuming the seesaw is supporting such force, it would an equilibrium system.
This is where we will take a detail look into rotational equilibrium
and torque ().
Have you ever try opening the door on the
hinge side? You need to push harder than if you push at the knob. This is
because the distance from your hand to the hinge (pivot point) is relatively small compare
to when you push from the knob. Product of the perpendicular distance drawn from the
pivot point to the point of action where force is applied and the force applied is called torque
Just as we define which direction is positive and negative for
x and y directions, we must define which direction of rotation is positive or negative for
torques. These symbols (, ) defines whether clockwise or
counter-clockwise is positive.
torque equations, you must choose the center of rotation first. It can be chosen
anywhere you want; however, you will find that in solving equilibrium problems, wisely
chosen centers of rotation can make getting the answer more simple.