The concept of impetus is similar to what we would call momentum (mv). However, whereas today we
consider momentum to be a measure of motion, impetus was thought to be the cause of motion. Albert of
Saxony, another scholar of this period, proposed that projectiles follow a path that has three phases: (1) an
initial period dominated by impetus, in which the object moves in a straight line in the direction it was
thrown; (2) an intermediate period in which impetus declines and natural motion begins to take over; and
(3) a final period in which impetus completely disappears and the object falls straight down.