> Joe Reid wrote:
> > A vector (or its reciprocal) times a scalar is still a vector. With
> > torque, the vector is the axis of rotation.
>
> As a vector requires both direction and magnitude, how can an axis be a
> vector?
>
It's a convenient formalism used in rotational mechanics. The vector points
along the axis *by convention*, with its direction indicating the
orientation of the axis, and it's magnitude indicating the rotational
velocity.
Of course that gives you two choices for which way it can point, depending
on whether the rotation is clockwise or counterclockwise. The convention
used, is that if your right-hand fingers curl in the direction of rotation,
then your thumb points in the direction of the vector (right-hand rule).
Thus if you're at a traffic circle in the US, the rotation vector points up
into the sky, if you're at a roundabout in the UK, it points down into the
ground. Not sure that's the best way to make traffic signs for the general
public though. <g>
Nat
