  When guns were developed in Europe in the 14th century, the theory of
projectile motion was not the one we are familiar with today due to Galileo and
Newton but the one taught by Aristotle approximately 1700 years earlier. In
addition to Aristotle's wide-ranging philosophical concerns, his theory arose
from the observation in everyday life that if an object is moving something
must be moving it. This idea works very well for the horse and cart but is
puzzling if you apply it to a thrown stone or spear. Problems with Aristotle's
theory of projectile motion were identified by one or two people between his
time and the 14th century, particularly John Philoponus (6th century AD) and
John Buridan (14th century AD). An archer or a spearman does not need a theory
of projectile motion, just a great deal of practice. But once the gun was
invented it became important to know what angle a barrel should be oriented at
and how much propellant to use, particularly as gunpowder was expensive.
However, for many years afterwards the manufacturing techniques used meant that
cannonballs were a loose fit to gun-barrels making cannons both inaccurate and
of poor reproducibility shot-to-shot. Also air resistance makes the trajectory
both impossible to calculate and qualitatively similar to theories based on
Aristotle's writings. It was not until Galileo and Newton worked on the problem
that a better theory of ideal projectile motion was arrived at.
