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Aristotle the Great
Logic rules over experimental
proof!!!
Aristotle the Vague
 That a final cause may exist among unchangeable entities is shown by
the distinction of its meanings. For the final cause is (a) some being
for whose good an action is done, and (b) something at which the
action aims; and of these the latter exists among unchangeable
entities though the former does not. The final cause, then, produces
motion as being loved, but all other things move by being moved. Now
if something is moved it is capable of being otherwise than as it is.
Therefore if its actuality is the primary form of spatial motion, then in
so far as it is subject to change, in this respect it is capable of being
otherwise,--in place, even if not in substance. But since there is
something which moves while itself unmoved, existing actually, this
can in no way be otherwise than as it is. For motion in space is the
first of the kinds of change, and motion in a circle the first kind of
spatial motion; and this the first mover produces. The first mover,
then, exists of necessity; and in so far as it exists by necessity, its
mode of being is good, and it is in this sense a first principle. For the
necessary has all these senses--that which is necessary perforce
because it is contrary to the natural impulse, that without which the
good is impossible, and that which cannot be otherwise but can exist
only in a single way. (Metaphysics, Book XII, Chapter 7, 1072)
Prime Mover

There is a privileged being: The Prime
Mover. He is the first agent, responsible
for moving objects, which, in turn, move
other objects.

The Prime Mover, he argued, must be at
Absolute Rest. By "absolute" rest , we
mean that all observers will universally
agree on that state of rest
Cosmology de Aristotle
Heavenly bodies have natural circular
motion because they are perfect and
unchanging
 Requires Ptolemaic Machine to rectify
observations against this proclamation
 With this machine, planetary predictions
could be made with good accuracy
 This gives the model real power
 No observation strongly rules out model

Analyze This

"Now since changes are of four kindseither in respect of the 'what' or of the
quality or of the quantity or of the place,
and change in respect of 'thisness' is
simple generation and destruction, and
change in quantity is increase and
diminution, and change in respect of an
affection is alteration, and change of place
is motion, changes will be from given
states into those contrary to them in these
several respects."
Aristotle’s Laws of Motion
 There is no motion without a force
 Speed is proportional to force and
inversely proportional to resistance
 Qualitatively this implies that a body will
traverse a thinner medium in a shorter
time than a thicker medium (of the same
length): things will go faster through air
than through water.
 Test this idea
Testing and Questions


Class Discussion Question: What is the
logical consequence of motion in a vacuum,
under this hypothesis?
For falling bodies, the force is the weight
pulling down a body and the resistance is
that of the medium (air, water, etc.).
Aristotle noted that a falling object gains
speed, which he then attributed to a gain in
weight.
Falling Objects
If initial weight determines the speed of
fall, then when two different weights are
dropped from a high place the heavier will
fall faster and the lighter slower, in
proportion to the two weights. A 10 lb
weight would reach Earth by the time a 1
lb weight had fallen one-tenth as far
 Oh yeah, sucker, prove it ….

Projectile Motion
In Aristotle's view, objects moved parallel
to the Earth's surface until it was time
(i.e. it was their destiny) to fall back to
the earth
 When a stone is thrown, an impetus is
given to it to disturb it from its natural
condition. Gradually the stone “forgets”
this impetus and falls back to its natural
place:

Aristotle’s Cannon
Experiments Show
 Aristotle’s logical thinking of motion and
falling bodies fails all experimental tests
universally.
 Indeed, Archimedes (~250 BC) realized
projectile motion was parabolic and devised
effective catapults to lob quarter ton stones
and those damn Romans