如图所示，这是一种“永动机”的设计方案，轮子中央有一个转动轴，轮子的边缘安装着12 个可以活动的短杆，每个短杆的一端装有一个铁球．方案的设计者认为，右边的球比左边的球离轴远些，因此右边球产生的力矩比左边球产生的力矩大，这样，轮子就会永无休止地沿着箭头所指的方向转动下去，并可以带动机器转动，你认为它真会那样吗？
解：虽然右边的球比左边的球离轴远些，但右边球的个数总比左边少，右边球产生的力矩并不会比左边球产生的力矩大，因此它不会沿着箭头所指的方向转动下去，其实它不消耗能量，却能源源不断地对外做功，本身就违反了能量守恒定律，这是不可能的．
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| In Twain, many people know what a "motorpool" means. It is 1 known as a place for the maintenance (维修) of official business and government cars. 2 it is a place for vehicle maintenance. More than ten years ago I came to America on business and I took advantage of the 3 to visit my friend. My friend drove a car to 4 me at the airport, and took me to his home. Out of the 5 , my friend drove his car into the innermost 6 , which had a sign "carpool only". I 7 what "carpool" meant. I felt doubted whether he was going to a motorpool. 8 I thought myself clever in asking: "Is there anything wrong with the car?" "Nothing. 9 ?" said he. "Well then, why are you going to carpool?" I 10 . My friend couldn't help 11 and told me that "carpool" refers to the lane that only the cars with two or more 12 can drive in. I felt rather embarrassed on 13 that. After dinner, my friend's neighbor came over to ask whether he 14 "carpool" the next day. " 15 ," my friend said, "I will accompany my friend to go shopping tomorrow." I was 16 again, wondering why he could not "carpool" with him since we had "carpooled" 17 . My friend explained to me again that the "carpool" that his neighbor 18 meant they in turn drove the car to work so as to save energy. The first "carpool" is a noun, 19 the second "carpool" is a verb. It is really 20 for newcomers in America to understand it in a short time. | ||||
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