问题 实验题

“验证力的平行四边形定则”实验中

(1)部分实验步骤如下,请完成有关内容:

A.将一根橡皮筋的一端固定在贴有白纸的竖直平整木板上,另一端绑上两根细线.

B.在其中一根细线挂上5个质量相等的钩码,使橡皮筋拉伸,如图甲所示,记录:________、________、________.

C.将步骤B中的钩码取下,分别在两根细线上挂上4个和3个质量相等的钩码,用两光滑硬棒BC使两细线互成角度,如图乙所示,小心调整BC的位置,使________________________________________________________________________,

记录__________________________________________________________________.

(2)如果“力的平行四边形定则”得到验证,那么图乙中=________.

答案

(1)B.钩码个数(或细线拉力)

橡皮筋与细线结点的位置O

细线的方向(说明:能反映细线方向的其他记录也可以)

C.橡皮筋与细线结点的位置与步骤B中结点位置重合

钩码个数和对应的细线方向

(2)从图中可得:

题目分析:(1)本题中是通过钩码的个数测量力的大小的,故需要记录钩码的个数,以及拉力的方向,即细线的方向

使用两个力拉动时,需要将绳子的接点拉到相同的位置,即橡皮筋与细线结点的位置与步骤B中结点位置重合,记录两个力的方向,钩码的个数

(2)从图中可得 ,表示水平方向上的分力,由于O点在水平方向上合力为零,故,所以

点评:本实验中的几个重点:(1)等效性:合力和分力的效果要相同,所以在实验中橡皮筋结点每一次都到同一位置.(2)记录合力的大小和方向.本实验通过钩码个数计算力的大小,力的方向由橡皮筋上取两点连线.

阅读理解

How long you live has a lot to do with your environment and lifestyle, but exceptional(特别的)long life may have even more to do with your genes. For the first time, researchers have discovered a genetic recipe(基因谱)that accurately predicts who may live to 100 and beyond.

Analysis shows that 90% of the participants who lived to 100 had at least one of the signature genetic clusters(标志基因组). Dr. Thomas Perls at the Boston University School of Medicine said, “We realize this is a complex genetic puzzle. There is a long way for us to go to understand how the integration(融合)of these genes—not just with themselves but with environmental factors—is playing a role in this long life puzzle.”

Perls has studied many factors that contribute to long life, and he is the first to acknowledge that living longer isn’t likely to be simply a matter of genes. His previous work has shown, for example, that among most elderly people who live into their 70s and 80s, about 70% can owe their long life to environmental factors such as not smoking; eating a healthy, low-fat, low-calorie diet; and remaining socially engaged and mentally active throughout life.

It seems clear that those who live extremely long are benefiting from a special DNA. In fact, Perls believes that the older a person gets, the more likely it is that his or her genes are contributing to those extended years.

小题1:Which of the following is TRUE according to Paragraph 2?

A.Most long-living people have special long-life-related genes.

B.Ninety percent of the participants lived to 100 years of age.

C.All the long-living people have only one signature genetic cluster.

D.Scientists know how the integration of the genes helps people live long.小题2: Perls may most likely agree that         .

A.most people living extremely long benefit from not smoking

B.living longer just depends on certain genetic recipes

C.environmental factors play an important role in long-living

D.being mentally active has nothing to do with living an old age小题3: Which of the following is FALSE according to the text?

A.Remaining socially engaged helps a person to live long.

B.A genetic recipe can accurately predict who may live to 100 and beyond.

C.Perls is the first to think living longer is just a matter of genes.

D.The older he gets, the more likely the genes contribute to his extended years.小题4:Which of the following would be the best title for the text?

A.Genes May Predict Who Lives to 100

B.Environment And Genes

C.Genes, the Secret of Long Living

D.Lifestyle And Genes

单项选择题