You can judge the nature of Aristotle's physics and why it was hard to test from this description: (from George Smoot, http://aether.lbl.gov/www/classes/p10/aristotle-physics.html)

Aristotle held that the universe was divided into two parts, the terrestrial region and the celestial region. In the realm of Earth, all bodies were made out of combinations of four substances, earth, fire, air, and water,* whereas in the region of the universe beyond the Moon the heavenly bodies such as the Sun, the stars, and the planets were made of a fifth substance, called quintessence.

Heavy material bodies like rocks and iron consisted mostly of earth with small parts of the other elements. Less dense objects were thought to contain a larger admixture of the other elements along with earth. For instance, humans consisted of a complex mixture of all the elements: earth, which gave material strength and weight; fire, which provided warmth; water, which accounted for blood and other bodily fluids; and air, which filled the lungs and provided the breath of life. Of course, some people were more earthly, fiery, airy, or watery than others. The Sun, planets, and stars were made of quintessence, a pure, perfect substance, quite unlike the elements found on Earth. The Moon, marking the boundary between the sublunary earthly region and the supralunary heavenly region, was mostly quintessence, but because of its proximity to Earth it was contaminated with a small admixture of earthly elements, which accounted for the visible imperfections on its surface.

The fundamental assumption in Aristotelian physics was that the natural state of sublunary matter is rest. Earth, air, and water must seek their natural place at rest in the center of Earth unless stopped by an impenetrable surface like the ground or a table. The natural place of rest of the element fire is somewhere above us (but well below the Moon). The air we see around us is a mixture of the elements air and fire (after all, air, at least in Greece, has warmth), so its behavior is complicated by the competition between the tendency for fire to rise and air to fall. Except in very complicated situations such as when air and fire were mixed together, motion was not a natural state of affairs.

Aristotle's model provided a simple, compelling explanation for falling rocks, rising flames, and the circulation of the air. However, it was less successful in explaining "violent motion" such as when an object is hurled from a catapult. To see why this would be a problem for the Aristotelian worldview, imagine the following experiment: Find a cat, and putt it from a siege machine. You would observe that the cat continues to travel through the air (before landing safely on its feet) even after it was no longer being pushed by the arm of the machine. If the natural state of motion of the cat is rest on Earth, why didn't the cat drop to the ground immediately on leaving the machine? Here, Aristotelian physics had to say that this kind of motion is different because it is "violent," and had to invent some mechanism to keep the cat in the air during violent motion. All of the mechanisms fall under the technical description "hand waving." One of the most popular explanations was that the air in front of the cat became disturbed by the movement of the cat, and swirled behind the cat and pushed it along. Thus, in Aristotelian dynamics, there was a distinction between "natural" downward motion (for example, a rock falling to the ground when dropped) and unnatural violent motion not directed toward the center of Earth (such as that resulting from a catapult).

*Here the elements are denoted by italics. Thus, earth is a pure element, whereas Earth is a planet made mostly of earth but also containing some of the other elements; air is a pure element, whereas the air we breathe is mostly air, but with some other elements mixed in.