When different forces act upon a particle, but its motion does not change with time, it is said to be in equilibrium. Equilibrium can be categorized as static or dynamic. If a particle is at rest, it is said to be in static equilibrium, and if it is moving with constant velocity, the particle is said to be in dynamic equilibrium. For a particle to be in equilibrium, it should satisfy two conditions simultaneously. First, the net force, the vector sum of all the forces acting on the particle, must equal zero. Second, the net torque acting on the particle about an axis passing through the particle must be zero, indicating that the net moment is also equal to zero. Consider two equal masses placed at the two ends of a wooden plank equidistant from its center. The plank's center is set on a cylindrical pivot. In such a condition, static equilibrium is established since the net force, and the net torque on the system is zero.