Originally Posted by shermaine

Hello,

May i know what cases to use dot product and cross product?
Pls advise.
Thanks.

If you google for +"dot product" +"cross product" you get plenty of hits, is there any electronic reason for the question?. Probably if you don't know which to use, you don't need them!.

cross product yields a vector quantity that is orthogonal to both vectors that you crossed

dot product yields a scalar quantity. a simple appliaction is work = F (dot) d
F(dot)d = mag(F) mag(d) cos THETA

so if you use that for work, you automatically get the component of the force that is doing the work (in the same direction)

good luck

david