In the 4th century, Aristotle developed the first systematic set of ideas to describe the natural world, often referred to as Aristotelian physics. In his research Aristotle made many discoveries regarding the dynamics of movement. He believed that the natural motion of an object was determined primarily by the nature of the substance that made up the object, in terms of the four basic elements: earth, air, fire, and water. Therefore a stone, when freed from the hand, fell to the ground because it was made of a substance similar to Earth. Likewise, the smoke rose into the sky because it wanted to be closer to the air and further from the Earth. Observing this, Aristotle concluded that natural motion resulted from the tendency of objects to return to their "natural" place and come to rest. He decided that objects inherently have a natural tendency to fall to the earth, which he called gravity, or a tendency to rise toward the sky, which he called levity. Aristotle also believed that heavier objects fall faster than smaller objects because the speed of fall is proportional to the weight of the object. The greater the mass, the greater the intrinsic natural tendency contained in the object that would bring it back to the surface of the Earth. This explained the movement of inanimate matter, attributing the movement to the “nature” of something that was obviously not alive. Aristotle distinguished between natural movement and forced or “violent” movement of non-living objects. Forced motion occurred when a mass was acted upon by some other object which caused it to move. For example, the natural tendency of a stone, if left unsupported, is to fall to the ground, but it can also be picked up or thrown. Aristotle called this… half the paper… equilibrium, resulting in a stagnant system. An example of Newton's third law is the tension in a string tied to a large mass. When the string is pulled, the person pulling exerts a force on the mass, while an equal and opposite force is applied to the person, causing the entire system to stop. The motion, therefore, resulted from an imbalance of overall force, as seen in Newton's second law of motion. Sir Isaac Newton was able to draw on Aristotle's misconceptions and Galileo's observations to generalize the three laws of universal motion. These laws changed the way the Universe was viewed and clearly showed the modern explanation of forces through its statements. Newton combined the research of many eminent scientists, including Aristotle and Galileo, to complete the mechanical theories now called classical or Newtonian mechanics..