Ah hah !
Newton's second law of motion:
Net force = (mass) x (acceleration)
If the object's acceleration is zero, then the right side
of that formula is zero.
If the right side is zero, then the left side is also zero.
That means the net force on the object ... the sum of
all forces that may be acting on it ... is zero. The whole
bunch of um have the same effect on the object as if
there were no forces at all.
