  This paper is a modern exposition of old ideas. The setting is a Euclidian
space $E$ of dimension $n$ with associated vector space $V$ of dimension $n$. A
(non-zero) sliding vector is a vector in $V$ that is free to move, but only
within a line $L$ of $E$. The set of sliding vectors has dimension $2n-1$. This
set is naturally embedded in a vector space of dimension ${n +1 \choose 2}$. An
element of this vector space will be called a line bivector. Other terms used
in applications are screw and wrench. There is a nice description of line
bivectors in terms of Grassmann algebra in a projective representation. It is
shown that this abstract description has a concrete realization in terms of
moment functions from $E$ to bivectors over $V$. The literature in physics and
engineering mainly deals with the special case $n=3$. The results of the paper
apply in this case and to its most common application, where the vectors in $V$
represent force and the bivectors over $V$ represent torque. It concludes with
a discussion of duality, such as that of force and velocity or of torque and
angular velocity.
