What kind of force can a rock exert which a motor cannot?

Question

Imagine a dam with two doors. We have two cases: First case: there is a rock heavy enough to stop the doors from opening. Second case: there are are two motors or kind of machines (not sure if it can be motors) applying force on the two doors enough to keep them closed. In the first case we do not consume energy (I guess!!) but in the second case we consume energy. How is that possible? What kind of force does the rock use to keep the doors closed, which the motors/machines cannot use? PS: I am 15 years old and I only know the basics of physics so keep it simple,please.

Answer 1

In both cases, you have a static situation (the door stays closed because the applied force is at least equal to the force associated with the water pressure.--it does not matter how the force is applied)

Energy comes into play only when a force acts through a distance. e.g.: If you pick up a rock, you have added potential energy, which is the product of the weight of the rock and the change in elevation.