自行车车轮的外表面都有凹凸不平的花纹，这是为了______，菜刀的刀刃要做得很薄，这是为了______．请根据下列物体尺度的大小、按照从小到大的顺序排列（只填序号）：①原子、②电子、③生物体、④太阳系、⑤地球：______．
自行车车轮的外表面都有凹凸不平的花纹，是为了在压力一定时，增大接触面粗糙程度来增大轮胎和地面之间的摩擦力，防止打滑．
菜刀的刀刃要做得很薄，是为了在压力一定时，减小受力面积来增大菜刀对物体的压强．
物体尺度从小到大的顺序排列：电子--原子--生物体--地球--太阳系．
故答案为：增大摩擦力；增大压强；②①③⑤④．
阅读下面对话，从方框内7个选项中选择5个恰当Li Meng is studying in a middle
B: Not yet. 小题1: A: I’m going to the bookstore. Would you like to go with me? B: Sure. 小题2: A: Well, I want to buy some story books. B: That’s great. What kind of stories do you like? A: 小题3: What about you?B: Me, too. My favorite book is The Old Man and the Sea. A: I know that book. 小题4: B: You are right. Have you read any books by young writers born in the 1980s? A: Of course, and I like reading their works on the Internet. B: Haha! 小题5: A: That’s right. |