Final answer:
The minimum number of axes required for analyzing an object falling straight down is one. This one axis represents the one-dimensional motion influenced by gravity which is constant and vertical, with the acceleration due to gravity denoted by g (9.80 m/s²).
Step-by-step explanation:
The minimum number of axes required in a frame of reference to analyze motion of an object falling straight down is one. This is because the motion is one-dimensional as gravity acts as a constant acceleration directly downward, which is considered one-dimensional motion involving gravity. The motion can be completely described with just the vertical axis (usually the y-axis), assuming no air resistance or friction are present, and thus velocity is vertical and acceleration is constant at g (9.80 m/s²).
An example to illustrate this is when an object is dropped, and its initial velocity is zero. After the release, the object is in free-fall, moving straight down with its velocity increasing at a constant rate due to the acceleration of gravity, g. Since there is no horizontal movement, no x-axis is needed to describe its motion.