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The ghastly pseudo-scientific form of physics that plagued Western Civilization up until the Reineissance. The theories put forth by Aristotle are very much descriptive of Aristotelian philosophy, whose credo is basically "seeing is believing". Under his system, an object at rest, if acted upon by a force, would take to motion and gradually return to rest by its own means. It also stipulated that heavier objects will fall at a faster rate than lighter objects (which Galileo easily disproved with his infinitely simple and amazingly famous cannonball experiment).

I would like to add extra emphasis to the 'seeing' part of the aforementioned credo; Aristotle didn't seem to investigate his theories very intensly. Even an ancient Greek, without the assistance of modern technology (or the scientific basis Newton built upon), could conclude that, for instance, the terrain a ball rolled on and the amount of wind present had something to do with the rate at which it rolled. Something as simple as rope-burn would easily explain the presence of something resembling friction. Well, that's enough of my anti-Aristotelian drivel. Just remember that he might have written some very inspiring words, but he's also written some very misguided ones...

I'd also like to point out that I pronounce it 'Air-ist-oh-teel-yan'.

In addition to what was said above, here are the main points of Aristotelian physics:

  • The realm of the Earth is corrupt, while the realm of the heavens is perfect. These realms follow completely different sets of rules. Rules and logic that appliy down here do not apply up there.
  • The heavens are perfect and made of quintessence. Quintessential motion is uniform and circular (this was actually proposed by Plato some time earlier). Nothing ever changes in the heavens besides the movement of the stars and planets (even the stars revolve around the Earth once every 24 hours, as opposed to standing still while the Earth rotates). The heavens are made of solid spheres of quintessence or crystal without any empty space between them because nature abhors a vacuum, and besides, why would the creator of the universe have put all that empty space there?(1)
  • There are 4 earthly elements: earth, water, fire, and air. Of the four earth is (usually) the heaviest, followed by water, air, and fire. Heavier elements will always sink within lighter ones according to Archimedes' principle.
  • The natural state of (earthly) matter is to be at rest at the center of the universe (and since Earth is the center of the universe, objects will fall toward it's center). Heavy objects have this tendancy more than light objects, so a heavy object will fall faster than a light one. This can be shown by dropping a rock and a feather at the same time.(2)
  • If you want an object to do something other than follow it's natural motion, you must apply a force. When you stop applying the force, the motion stops, unless you apply a lot of force, in which case you will give the object impetus, which causes motion to continue, and will be used up as it causes the object to move. When the object runs out of impetus it will return to its natural state. Therefore, if you throw a ball, it will go in a straight line until it runs out of impetus. Then it will fall straight down.(3)

    All motion is absolute. If you are on a moving platform, and drop an object, it will land directly below the point from which you dropped it, relative to the earth (which is stationary). If you drop a ball from the top of the mast of a ship, it will land off to the stern.(4)

the laws of Aristotelian physics were used as arguements against the Copernican system of the cosmos, which included a moving Earth. As Christopher Clavius pointed out in his book, De Sphaera, when you drop a ball from the mast of a moving ship, the ball falls to the stern. If the earth really was turning, then an object dropped from about 16 feet would land 1000 feet to the west (since the surface of the Earth moves at about 1000 feet per second to the east due to the Earth's rotation).


Notes:

  1. Nature does abhor a vacuum. This is why a vacuum pump works. But a vacuum pump at sea level can only pump water up to about 24 feet. After that, atmospheric pressure is not enough to cancel out the weight of the water, and there will be a vacuum between the water and the piston.
  2. Yes, Galileo did disprove this with a couple of heavy cannonballs of different weights. But this should have been disproved a thousand years earlier with a simple thought experiment: What happens if you tie two objects together? Do you count them as two objects or as one? According to Aristotle, the light object will fall more slowly, and, being attached to the heavy one, will slow it down. But if you consider them a single object, together they will be heavier than either alone and should fall faster.
  3. Any kid who's ever played catch can tell you that that is not how a ball moves when it is thrown. They'd tell you that it follows a smooth curve.
  4. Aristotle must never have tried to juggle while moving. If he had, he'd have found out that to have the balls land in his hands, he should throw them straight up, and they will continue to move forward with him. According to his physics, however, one would have to throw the balls ahead of them. If you try this, you will find yourself accelerating.

Seeing as how easily Aristotle's laws of physics can be disproven (watch someone throw a ball), it's hard to understand how they could have been accepted for as long as they were. Apperently people didn't actually try to connect them with the real world, or they surely would have been replaced in a minute. It wasn't until the Renaissance that some people (most notably Galileo) figured that it might be a good idea to see how things really work.

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