The calculator can stay balanced on the edge of the table. It can stay balanced not because there are equal masses on both sides of the edge (fulcrum), but because the torques are the same. Torque = Force x lever arm distance. When the torques cancel each other out, the object is at rotational equilibrium. This can either mean the object is at rest or the object is rotating at a constant speed.The mass of the calculator lies solely on the center of mass. If the center of mass is not supported by the fulcrum, then the distance between the center of mass and the fulcrum is the lever arm distance.
Many things in every day life uses torques. Turning the knob to open a door uses a torque and so does turning the steering wheel in a car.
