The oil lamp on my dresser is at equilibrium. But though it is at equilibrium, there are forces acting upon it. The earth is pulling the lamp down and, in accordance with Newton's Third Law, the lamp is pulling the earth up. The lamp is pushing the box down and the box is pushing the lamp up. The air is pushing the lamp left and the lamp is pushing the air right, and so on and so forth. How can a lamp be at equilibrium with all these invisible forces at play, you ask? Well, because the forces acting on lamp are equal and opposite. Furthermore, even as the lamp pulls the earth up, to use a popular example, the earth's mass is so enormous than when plugged into the equation acceleration= net force/ mass, the division of the net force by so huge a number results in an acceleration so small it is negligent. What a pity. That is for lamp.