Question

Notice that we have the weight of the crane exerting a torque about the front wheels of the same crane. to create a torque, a force must be present, so it would seem that somehow the weight of the crane is exerting a force upon its front wheels. however, the crane is one object, and it follows from newton's laws that an object cannot exert a net force upon itself. this crane seems to be defying newton's laws. what's going on here?

Answer 1

According to Newton's third law of motion, "For every action, there is an equal but opposite reaction." The force exerted by one object on a second object would produce a reaction that is exerted by the second object to the first object. It's not the first object that is exerting the net force upon itself. No laws of physics are defied.