American Scientist

Opening a door equipped with a familiar round doorknob is something that most of us learn to do as children, even though one small hand might not fully encompass the knob. No matter, for we can use two hands until we grow up and can finally grasp the knob easily with one. In either case, using a doorknob is a haptic act aided by an aural cue: We turn the knob until we feel and hear the latch bolt slide free of the strike plate attached to the doorjamb. When this happens, we change our hand’s twisting motion to a pulling or pushing one that causes the door to swing open.