本篇talk 主要給大家上了一堂“物理”課，講解了有關(guān)“重力”的話題。人們會想當(dāng)然地以為重力是物體的自然屬性，是不變的衡量。文章指出，這是錯誤的觀點(diǎn)。物體的重力和地球?qū)ζ涞囊τ嘘P(guān)，當(dāng)物體離開地球，比如去了月球，它的重量也會改變。這是因?yàn)樵虑虮鹊厍蛐。鼘ξ矬w的吸引力也比地球?qū)ξ矬w的吸引力小。文章雖然是學(xué)術(shù)類話題，但此物理原理大家一般都比較熟悉，相信理科還不錯的同學(xué)應(yīng)該沒有大問題吧。

We are so used to our life on the surface of the earth that it is not easy for our minds to break free of all the ideas that we take for granted. For example, we can feel things are heavy, so we think of weight as being a fixed quality in an object. But actually, it is not fixed at all. If you could take a one-pound packet of butter four thousand miles out from the earth, it would weigh only a quarter of a pound. The reason for such a change of weight is this: all objects have a natural attraction for all other objects. This is called gravitational attraction, but this power of attraction between two objects gets weaker as they get farther apart. So the weight of an object on the surface of the earth is not the same as its weight 4000 miles out in space. What about the weight of a one-pound of butter on the surface of the moon? There won’t be attraction between the butter and the moon, but the butter will weigh only about 1/6 as much as it does on the earth. This is because the moon is so much smaller than the earth. The amount of a gravitational pull that a body produces depends on the amount of material in it. A packet of butter has a gravitational pull of its own, but it is very small in relation to the pull of something as large as the moon or the earth.

Q23: According to the speaker, what quality of an object is taken for granted by people?

Q24: How much will a pound of butter weigh if it is brought 4000 miles into space?

Q25: What is the gravitational attraction?

Q26: Why does an object weigh much less on the moon than it does on the earth?