## Torque ( "Rotational Force" )

Remember, torque is a

vector.When we writeor

randFarevectorsand their "cross product" or "vector product" isalsoavector!We determine thedirectionof the "cross product" or "vector product" by yet another version of the "right hand rule".Draw a vector

rfrom the axis of rotation to the location of the forceF.To evaluate a cross product such as we must

the vectorsredrawrandFso they begin at acommon origin:Now

rotatethefirstvector,r, into thesecondvector,F,using the fingers of yourright hand (!).The new vector, tau , now points in the direction of your thumb!The

orderis important in a "cross product" or a "vector product".C=AxB

D=BxA

C= -D

AxB= -BxAThe "cross product" or "vector product" does

commute!not(c) 2002, Doug Davis; all rights reserved

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