First Condition for Equilibrium

What is equilibrium?  Equilibrium exists when an object doesn't change its motion, i.e. it doesn't accelerate.  Thus it can be stationary or moving at constant velocity.

As we have already seen, if we add up the forces on an object and they sum to zero, then the object does not change its motion.  This is called the first condition of equilibrium.

                net F = 0

It is a necessary criteria for equilibrium, however it is not sufficient.

In order to have equilibrium, two conditions must be met.
Speaker3.wmf (6408 bytes) First Condition for Equilibrium
* Remember that F is a vector quantity: Look at net F in x and net F in y, both are equal to zero