Equilibrium of particles

One of the most fundamental concepts within mechanics is that of equilibrium. An object is in equilibrium when the net force (and moment) acting upon it is zero. In M1 we only need to work with equilibrium of forces.
When there is zero net force on an object the object will not accelerate or change direction but will continue to move in a straight line with constant velocity or remain at rest.
Resultant forces are used to find the net force at a point. This will enable you to check whether or not a particle is in equilibrium.