Screws don't really support the weight of the object they are holding. They pull that object into the wall. The resulting friction is what holds most of the weight.
To see this, try loosening the screw, and notice how it quickly looses the ability to resist forces perpendicular to the screw; whereas it's ability to resist forces in the direction of the screw is largely unchanged.
Screws don't really support the weight of the object they are holding. They pull that object into the wall. The resulting friction is what holds most of the weight.
To see this, try loosening the screw, and notice how it quickly looses the ability to resist forces perpendicular to the screw; whereas it's ability to resist forces in the direction of the screw is largely unchanged.