While the main wheels are on the ground, any force from the bump will be transmitted through them to the airframe. Any such force will act as a torque around the center of gravity (CG).
The initial impulse will come from forward of the CG AND forward of the center of lift, so the forward part of the airplane will be "bumped" upward initially. If we just consider the vertical component of that force, inertia will tend to cause the center of gravity to continue in its previous direction (no vertical movement), causing a rotation around the CG -- a "pitch up" as the tail goes down to compensate for the rising nose.
OTOH, there is also a horizontal drag force acting on the bottom of the wheel, trying to "trip" the airplane and pitch it nose down. If the ramp of the bump is shallow enough, the horizontal force/moment will be relatively small, and the vertical force will predominate. If the drag force is large, though (e.g., running into a lip/ledge just less than half the height of the tire), it may predominate and cause the airplane to nose over.
Another consideration would be how "tall" the airplane is in relation to its length. The vertical component of the lever arm between a tall landing gear strut and the CG could be substantial, exacerbating the "tripping" of nose-down tendency. OTOH, in a low-slung airplane with an aft CG, the horizontal lever arm would predominate, emphasizing the pitch-up tendency.
This analysis takes no balance weights, pilot reaction, or reflex into account.