are pressed against one another. By rubbing a finger against these grooves on the side, one can also introduce a horizontal alternating driving force where is a phase shift (describing the lag time between when the grooves contacts the moving rod, and finger respectively) and, again, X is some unknown scaling factor. Importantly, is the same frequency, and the two driving forces are said to be phase locked. The confluence of two phase matched driving forces in orthogonal directions gives rise to a rotational force on the centre of mass at the propeller end, and thus, rotation. When the operator of the whammy-diddle surreptitiously changes the side at which their finger contacts the stick (e.g. by contacting with the thumb instead of the fore-finger, or by changing the side at which a finger contacts the grooves of the base) they change the sign of the phase , and thus reverses the rotation. See also Whirligig References "Toys, Making a Whammy Diddle", MUGWUMPS, Vol. 1, No. 6, November 1972. Further reading Schnacke, Dick. American Folk Toys: How to Make Them, Viking Press, 1974. () External links Physics - Gee-Haw Whammy Diddle - YouTube Technique - Gee-Haw Whammy Diddle - YouTube Folklore - Gee-Haw Whammy Diddle - YouTube Traditional toys Wooden toys