问题 实验题

(1)在“验证力的平行四边形定则”实验中,用两个弹簧测力计分别钩住细绳套,互成角度地拉橡皮条,使它伸长到某一位置O点,这一步操作中必须记录的是(   )

A.橡皮条固定端得位置

B.描下O点的位置和两细绳的方向

C.橡皮条伸长后的总长度

D.两个弹簧测力计的读数(2)做实验时,根据测量结果在白纸上画出如图所示的图示图中O为橡皮条与细绳套的结点,图中________是F1和F2的合力的理论值;________是F1和F2的合力的实际测量值

答案

(1)BD (2)F’   F

该实验的实验目的是验证力的平行四边形定则,要根据两个弹簧拉橡皮筋时两个拉力的大小和方向做出平行四边形求出其合力大小,然后与一个弹簧拉橡皮筋时的拉力大小进行比较,最后得出结论,故需要记录的是两弹力的大小和方向,故AC错误,BD正确.

故选BD.

(2)F1与F2合力的实验值是指通过实验得到值,即用一个弹簧拉绳套时测得的力的大小和方向,而理论值(实际值)是指通过平行四边形得出的值,故F′是力F1与F2合力的理论值,F是F1和F2的合力的实际测量值.

故答案为:F′,F.

单项选择题
单项选择题

In 1993, New York State ordered stores to charge a deposit on beverage (饮料) containers. Within a year, consumers had returned millions of aluminum cans and glass and plastic bottles. Plenty of companies were eager to accept the aluminum and glass as raw materials for new products, but because few could figure out what to do with the plastic, much of it wound up buried in landfills (垃圾填埋场). The problem was not limited to New York. Unfortunately, there were too few uses for second-hand plastic.

Today, one out of five plastic soda bottles is recycled (回收利用) in the United States. The reason for the change is that now there are dozens of companies across the country buying discarded plastic soda bottles and turning them into fence posts, paint brushes, etc.

As the New York experience shows, recycling involves more than simply separating valuable materials from the rest of the rubbish. A discard remains a discard until somebody figures out how to give it a second life—and until economic arrangements exist to give that second life value. Without adequate markets to absorb materials collected for recycling, throwaways actually depress prices for used materials.

Shrinking landfill space, and rising costs for burying and burning rubbish are forcing local governments to look more closely at recycling. In many areas, the East Coast especially, recycling is already the least expensive waste-management option. For every ton of waste recycled, a city avoids paying for its disposal, which, in parts of New York, amounts to savings of more than $100 per ton. Recycling also stimulates the local economy by creating jobs and trims the pollution control and energy costs of industries that make recycled products by giving them a more refined raw material.

The returned plastic bottles in New York used to ().

A. end up somewhere underground

B. be turned into raw materials

C. have a second-life value

D. be separated from other rubbish