Straight line vectors are useful in statics: Where their lengths depict
the magnitude of forces acting at points, and the arrowheads depict
Only one straight line vector is really useful in dynamics, where its
length depicts the initial [ reference] velocity at the start of a
problem, and the arrowhead depicts the direction.
This vector serves as an initial _reference_ velocity; from which all
_changes in velocity_ [s] - changes in speed and/or direction -
proceed; in proportion to, and in the direction of the thrust [f]
acting to cause the change, proceed; so that the resultant motion that
we "see" is a combination of the initial velocity [vi] multiplied by
its duration [t], and the change in speed or direction [s]:
So that the resultant motion - that we "see" - is [d/t = vi*t + s]. The
resultant change in position - that we "see" - is [d = vi+s]. Where,
for linear motion, d may be a displacement [s] - an increase or
decrease in l, or a displacement in direction; numerically equal to the
magnitude of the thrust [f] causing it.
Newton et al depicted curved motion as a series of infinitesimal
straight lines, which led to the infinitesimal calculus; because it
wasn't known yet that curves consisted of elliptical and geodesic
Now we know that motion does not consist of infinitesimal straight
lines, because right off the bat, atmospheric friction begins slowing
it, and gravity begins deflecting it.
Gravitation is universal; there is no place where it can be escaped;
except in our imagination.