『新东方在线托福听力』为托福考生准备了ETS托福TPO/【学术讲座】#12听力练习，【学术讲座】#12原文答案解析，【学术讲座】#12听力原文练习音频翻译。

托福TPO/【学术讲座】#12听力原答案解析-音频翻译【新东方在线】

Using Aristotle's system of classification, which primary substance is the densest?

According to the speaker, what types of motions does Aristotle's theory try to explain?

According to Aristotle’s theory, why does smoke rise?

Listen to a short talk on history.OK. Since we’ve been talking about mechanics and then we still have a few minutes. Let me tell you a little about the ancient Greeks and what they thought about mechanics. They came up with a system that for them seem to describe and explain the different motions of different materials. More than 2000 years ago, Aristotle, the ancient Greek philosopher, assumed that all the matter on earth were made up of four prime substances, earth, water, air and fire. Under this system, earth is the densest, water is the next, air is less dense than water, and fire is least dense of all. The heaviest object was made of earth and water, and lighter object contains significant amounts of fire or air. So when Aristotle observed that different types of matter had different characteristics. He assumed this was because the different types of matter were composed of different amounts of four primary substances. And Aristotle believes that the motions of objects could also be explained by the basic natures of four primary substances. Hum, for example, there was a basic motion of up or down. Aristotle noticed that when he released most objects, they would drop downwards. But he also knew that something would rise upwards, like smoke. Aristotle considered an object downward or upward motion to be the result of dominant nature of the object. So according to Aristotle, matter like rock were primarily composed of earth, therefore, they naturally want to move toward the center of the earth because this was all thing earthly rested. But fire had a different resting place, the sky. So smoke would naturally rise when it was released because it was driving toward its natural resting place.

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