
210 Ballistics: Theory and Design of Guns and Ammunition
Now, if we examine the particle as moving in two dimensions only, we can break its motion
up into two components, one parallel to and one perpendicular to the position vector, r
(Figure 7.8). The position vector written in this coordinate system is given by
(7.28)
So from our denition for the velocity in Equation 7.26, we get
v
e
== +
r
r
r
(7.29)
Since e
r
is a unit vector (its magnitude is a constant = 1) the only thing that changes with
time is its direction.
This introduces the concept of curvilinear motion with radial coordinates, (r, θ). The
direction is dened by the angle, ...