电灯开关绳如能伸缩才方便。有人在绳的两端装上磁铁,不用时可使绳长度缩短一半。但若不用磁铁,怎么办才能这样呢? 【提示】 (1)绳子挂到上边的环上,使其来回滑动。 (2)只用绳子不行吗? 答: 使用两个小球。下面的球系上绳,上面的球挖个洞,穿上绳子,把环从下面穿过去,固定在小球上。一拉上面的小球,灯绳就会缩短,一拉 Light switch rope if it is easy to retractable. Someone has magnets on both ends of the rope, reducing rope length by half when not in use. But if you do not use a magnet, what can you do? [Hint] (1) The rope is hung on the upper ring to slide back and forth. (2) only use the rope? A: The use of two small balls. The ball below the line on the rope, dig a hole above the ball, put on the rope, the ring through from below, fixed on the ball. A pull the ball above, the light rope will be shortened, a pull