Aristotle the Great

1
Aristotle the Great

• Logic rules over experimental proof!!!

2
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)

3
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

4
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

5
Analyze This

• "Now since changes are of four kinds-either 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."

6
Aristotles 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

7
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.

8
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 .

9
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

10
Aristotles Cannon
11
Experiments Show

• Aristotles 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