题目

Dear Editor,     I am writing tell you about the discussion we’ve had about whether it is necessary of middle school students to have mobile phones. Most students think this is more convenient for them to keep in the touch with their parents and classmates. And what’s much, it’s a fashion. However, most teachers think middle school students are not old enough to control them. It is a waste of time for students to play games and sending massages on their mobile phones. Therefore, it is easy to make students contact with each other. In my opinion, following the fashion was underst（1）如图1，小球沿粗糙斜面滚下，画出小球的受力示意图．（2）如图2，画出静止在光滑台阶上的铁球的受力示意图．