What condition defines static equilibrium?

Static equilibrium is defined by two key conditions that must be met simultaneously: the net force acting on an object must be zero, and the net torque acting on that object must also be zero.

When the net force is zero, it ensures that the object is not accelerating—meaning its velocity remains constant (which could be zero if the object is at rest). This prevents any linear motion, maintaining the object's position in space.

Simultaneously, when the net torque is zero, it ensures that there is no tendency for the object to start rotating. This means that if the object is not already rotating, it will remain stationary, and if it is rotating, it will not change its angular velocity.

Both of these conditions are crucial for an object to be in static equilibrium. If either the net force or the net torque is not zero, the object would either move linearly or rotate, respectively, thus not meeting the criteria for static equilibrium. Therefore, the correct answer encompasses both conditions—confirming that an object in static equilibrium is not only stable but also unchanging in its state of motion.