题目

完形填空 One of the founding fathers of the Internethas predicted the end of traditional television. Vint Cerf, who helped to buildthe Internet while working 1 aresearcher in America, said that television was 2its iPod moment. In the same way that people now 3 theirfavorite music onto their iPod, he said that viewers would soon be downloading mostof favorite programs 4their computers. Mr Cerf, who is now the vice-president of Google,says that, You're still going to need5television for certain things—like news,sporting events and emergencies—but 6it is going to be almost like the iPod,w15．某实验小组利用如图所示装置研究杠杆的机械效率，实验的主要步骤如下：（1）用轻绳悬挂杠杆一端的O点作为支点，在A点用轻绳悬挂总重为G的钩码，在B点用轻绳竖直悬挂一个弹簧测力计，使杠杆保持水平；（2）竖直向上拉动弹簧测力计缓慢匀速上升（保持O点位置不变），在此过程中弹簧测力计的读数为F，利用刻度尺分别测出A、B两点上升的高度为h1、h2．回答下列问题：①杠杆机械效率的表达式为η=$\frac{G{h}_{1}}{F{h}_{2}}$×100%．（用已知或测量的物理量符号表示）②本次实验中，若提升的钩码重一定，则影响杠杆机械效率的主要因素是：杠杆自身的重力．③若只将钩码的悬挂点由A移至C，O、B位置不变，仍将钩码提升相同的高度，则杠杆的机械效率将变大（选填“变大”、“变小”或“不变”）．