  This work introduces screw theory, a venerable but yet little known theory
aimed at describing rigid body dynamics. This formulation of mechanics unifies
in the concept of screw the translational and rotational degrees of freedom of
the body. It captures a remarkable mathematical analogy between mechanical
momenta and linear velocities, and between forces and angular velocities. For
instance, it clarifies that angular velocities should be treated as applied
vectors and that, under the composition of motions, they sum with the same
rules of applied forces. This work provides a short and rigorous introduction
to screw theory intended to an undergraduate and general readership.
