"1" . . . . . . _:vb7034328 "2012 March, Henry Petroski, \u201COpening Doors\u201D, in American Scientist\u200E[1], volume 100, number 2, pages 112\u20133:"@en . . . . . . . . _:vb7034328 "A doorknob of whatever roundish shape is effectively a continuum of levers, with the axis of the latching mechanism\u2014known as the spindle\u2014being the fulcrum about which the turning takes place. Applying a force tangential to the knob is essentially equivalent to applying one perpendicular to a radial line defining the lever."@en . _:vb7034328 . . _:vb7034327 . . _:vb7034327 "in essence"@en . .