Scientistsstudythenaturalworldbyusing“scientificm...

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Scientists study the natural world by using “scientific method”. When a scientist observes some phenomenon in nature, he develops an idea, called a theory or hypothesis (假设), about what is happening. Then he does an experiment to test his theory. If the results are as expected, then the experiment proves the hypothesis which makes it more likely that the theory is correct. If the experiment fails and the results are not as expected, then the scientist must come up with a new theory that he can test.

In ancient times great thinkers came up with complicated theories to explain nature, but they did not always prove them by experiment. For example, the great Greek thinker Aristotle, had a theory that heavy objects would fall faster than light objects. People believed this until the scientist Galileo performed an experiment and found it was wrong.

Here’s an experiment that you can use to prove or disprove a common-sense theory:

Step 1: Get an empty bottle with a small neck. A diameter (直径) of 1/2 inch should be ideal.

Step 2: Cut a sheet of paper to a square 5 inches on each side.

Step 3: Crumple (压皱) the paper into a tight wad (块状物).

Step 4: Lay the bottle on its side and place the paper so it lies loosely in the neck of the bottle.

Construct a theory about what will happen if you put your mouth about a half inch from the neck of the bottle and blow hard towards it. A common-sense theory might be that the wad would be blown into the bottle by the force of the breath. Now do your experiment to see what really happens.

If your theory was that the wad would be blown by the force of the air into the bottle, the experiment gave you unexpected results. In most cases the wad is blown out of the neck of the bottle in the opposite direction. A new theory might be that the air being blown into the bottle creates a whirlwind (旋风) of air currents (气流) in the closed space which push the wad out.

29. The writer mentions Aristotle’s theory to show ________.

A. he was a greater thinker in ancient times

B. he was less successful than Galileo

C. objects of different weights fall at the same speed

D. experiments are necessary to support theories

30. According to the passage, what is not required in the four–step experiment?

A. A pair of scissors. B. A piece of paper.

C. A bottle. D. A strong breath.

31. What’s the best title for the passage?

A. Come to Nature with Scientists B. Make up a New Theory

C. Experiment with Breath in a Bottle D. Watch Out for Common Sense

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