Stress
(17) Stress means a force acting across a unit area in a solid material in resisting separation, compacting, or sliding that tends to be induced by external forces. (18) Top of the mower's handles means the uppermost portion(s) of the handle that would be gripped by an operator in the normal operating position. (19) Walk-behind power lawn mower means a grass cutting machine either pushed or self-propelled, with a minimum cutting width of 12 in (305 mm) that employs an engine or a motor as a power source and is normally controlled by an operator walking behind the mower.