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A right-handed screw (the normal kind) must be turned clockwise into the wood (viewed from its head).

Carpentry of Vectors

Hand and Screwdriver Wood Screw

The cross product of two vectors is perpendicular to both; the right hand rule picks the one out of two possible perpendicular directions.

The diagrams show the right hand rule. The order of operands is important. The result of u × v points in the same direction a screw must point if twisting from u to v drives it into the wood.

Or, think of the direction your thumb points when your fingers curl around from u to v.


Does   u × v   point in the same direction as   v × u  ? (Hint: get out your screw driver).