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一、知识结构二、基础知识（一）简单机械1．杠杆（1）几个概念①杠杆—能绕着固定点转动的硬棒。可以是直的，也可以是弯曲的。②支点—杠杆绕着其转动的固定点。③动力—作用在杠杆上使其转动的力。④阻力—作用在杠杆上阻碍其转动的力。⑤动力臂—从支点到动力作用线的垂直
First, knowledge structure Second, basic knowledge (a) simple machinery Leverage (1) Several Concepts 1 Lever - A hard bar that can rotate around a fixed point. It can be straight or curved. 2 fulcrum—the fixed point around which the lever rotates. 3 Power - The force acting on the lever to turn it. 4 Resistance—The force that acts on a lever to hinder its rotation. 5 Power Arm - Vertical from fulcrum to power line of action