Theories of Motion Through Time
Greek Thought
Aristotle (384-322 B.C.E.)
• Was a very important Greek
philosopher
• Tutored Alexander the Great
• Thought rather than
experimented
• Was a student of Plato,
although he disagreed with
many of Plato’s ideas
• Studied all aspects of the
world; both philosophical and
physical.
• Could be thought of as a
“natural philosopher”
Circular Motion
• According to Aristotle, all objects had a natural
place.
• Earth was at the center, water above, and air
surrounding that.
• There was a fire layer outside the air layer, with
a mystical ether outside that
• All objects desired to find their natural place.
(Earthly objects fell, Fire like objects floated)
• Planets and stars moved in circles in the ether
The Universe
Thinking on Motion
• To him natural motion
on earth was in
straight lines toward
the center of earth.
• Violent or chaotic
motion required the
input of force (any
non natural motion is
violent i.e. horizontal
Why experiment when you can
motion)
just sit and think about it?
Motion of launched
objects according to
Aristotle. The arc
observed was
explained as a
transition from one
straight line to
another. (Not how
an object really
moves)
Aristotle’s cannon ball (sort of)
• The ball would have experienced a
slight curve at the “corner” of its travel
as it transferred from horizontal to
vertical. (From violent to natural Motion)
Violent Motion
• Any motion other than natural motion was
violent according to Aristotle.
• This motion required a push (or it would
stop moving)
• An object stopped once the force of the
push you gave it was used up.
Heavier = Faster
• Another idea of
Aristotle’s was that
heavier objects fell
faster as they rushed to
their natural position
closer to the center of
the earth (the center of
the universe)
Major Points
• According to Aristotle:
All motion of objects is in a straight line to
their “natural position” (Earthly objects fall,
heavenly objects rise).
Objects not moving naturally must be
constantly pushed or pulled or they will
instantly stop moving.
Heavier objects fall faster than lighter ones.
The Legacy
• Due to Aristotle’s vast influence on
philosophy, science, and physics his ideas
were not questioned for almost 2000
years.
• It took an Italian scientist named Galileo
Galilee to turn Aristotle on his ear and
correct two millennia of misconception!