Final answer:
An object is in static equilibrium when the net force and net torque acting on it are both equal to zero. Examples of objects in static equilibrium include a motionless person standing upright and a uniform plank resting on a level surface.
Step-by-step explanation:
In physics, an object is in static equilibrium when it is completely motionless and the net force and net torque acting on it are both equal to zero.
One example of an object in static equilibrium is a motionless person standing upright. The forces acting on the person, such as the weight of their body and the normal force exerted by the ground, add up to zero. Similarly, the torques acting on the person, such as the torques due to gravity, also balance out.
Another example is a uniform plank resting on a level surface. When the right amount of mass is placed at its right end, the plank remains balanced and does not tip over, satisfying the conditions for static equilibrium.