Why Do Rocking Chairs "Walk"?

Rocking chairs rest and rock on narrow bands along the bottom edges of the rockers.  If these bands of contact are skewed from perfect symmetry, then one rocker may take a little bite with each rocking repetition, moving the chair a bit.  Some number of rocks will move that chair an inch and on.  In order for a rocking chair to not move at all  (on a perfectly flat floor), the plane, curve, section, and symmetry of the rockers would have to be mathematically precise.  This we can not do, and floors are not mathematically flat either.  But our rockers must be symmetrical enough to get acceptable numbers of rocks to the inch of movement, because other than one chair we tuned up, the cause of movement has been the nap of rugs.  Some rugs have a directional nap.

When we built the showroom, we chose a commercial carpet for its color and tight weave. These were not sufficient criteria to use for choosing a rocking chair showroom floor.  Every rocker in the room moves toward the northeast, no matter which way they face.  Someone showed me this trick:  Lay a piece of paper on the floor.  Lay a pencil on the paper.  Roll the pencil back and forth with the flat of your hand.  If the rug has a directional nap, the paper will move in the same direction  (by the compass) no matter how you orient the pencil.  A rocking chair is likely to move in that direction as well.  I rather wish the carpet in the showroom wasn’t wearing like iron.  I am not temperamentally suited to changing it until it wears thin at the door, but when I do, I am taking paper and pencil to the store.