我们知道，许多物理实验要求在水平面上进行，请你应用不同的物理_爱下问搜题

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问题问答题

我们知道，许多物理实验要求在水平面上进行，请你应用不同的物理知识，设计两个简易实验，判断某狭长的直轨道是否水平，并完成下表．

	简要的操作步骤和判断轨道是否水平的方法	该方法所依据的主要物理原理
方法一
方法二

答案

可以利用水平面总跟重力方向相垂直的原理，也可利用连通器原理；

具体操作方法和原理如表格所示：

	简要的操作步骤和判断轨道是否水平的方法	该方法所依据的主要物理原理
方法一	利用一丁字形支架，在竖直杆上挂一重锤线，将支架的水平面放到长直的轨道上，如果垂线与杆子平行，则轨道是水平的．	重力的方向是竖直向下的，与竖直方向垂直的方向为水平方向．
方法二	用以U形管内装入适量的水，将水平与被测垂直轨道对齐，如果水平一垂直轨道是平行的，则长直轨道是水平的．	U形管内水静止时，水面总是水平的．

完形填空

Frank was walking down the 6th Street on a hot sunny day when he saw smoke coming out of the street. He could        the smoke, and it was getting thicker. Seeing the smoke coming out of a storm drain(雨水沟), Frank called the fire department immediately. “The storm drain is       fire!” he said. The fire department asked for his whereabouts and he said he was near the 6th and Main. They said they        be right there to investigate the situation. Frank needn’t to go anywhere, so he waited for the        to arrive. He was curious what could be burning beneath the street. As far as he knew, there wasn’t anything beneath the street        concrete(混凝土). And everyone        that concrete doesn’t burn.
A fire truck arrived a few        later. “Are you the man who     ?” asked the driver. “Yes. ” Frank answered. By now Frank could not only smell the        but also hear crackling sounds, just like wood burning. The firemen didn’t seem to consider it an emergency. “      do you think it could be?” Frank asked the driver. “Oh, we know what it is. We have to        a problem like this every few months. It’s the homeless people in their “     ”. ”
Homeless people have been living under the streets for years.       their knowledge of the storm drain system, they        their own “houses” beneath the streets. These living areas have tables, mattresses, chairs, and sofas. The settlers often “borrow” electricity by connecting to a live wire above ground to        their own lights and even TVs underground. Either this        electricity or a cigarette can cause an occasional fire.
Frank watched        some firemen lifted a manhole cover (井盖) and went beneath the street with a fire hose (消防软管). Then a few minutes later, the        smoke turned white. Shortly       , the firemen reappeared with a       person who seemed to have just been woken up.

C．investigated

C．storm drain

问答题简答题

空的主要内含是什么？