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例1.图1所示,杠杆 AB 可绕 B 点转动,在A端挂一重为 G 物体,并用细线系住 A 点,当AB 保持水平,细线和 AB 成30°角,则拉细线的力 F 等于___.(杠杆的自重不计)解:由支点和力臂的定义知,B 点是杠杆AB 的支点,AB 是杠杆的阻力臂.过 A 点作动力 F 的作用线 AC,再过 B 点作 AC 的垂线 BD,D 是垂足,则 BD 是动力臂.根据杠杆的平衡条件有 F·BD=G·
Example 1. As shown in Fig. 1, the lever AB can be rotated around point B. Hang a weight G object at the A end and pin point A with a thin wire. When AB is kept horizontal, the thin wire and AB become 30°, then the tapering is The force F of the line is equal to ___. (The weight of the lever is not counted) Solution: Known from the definition of the fulcrum and the arm, point B is the fulcrum of the lever AB, AB is the arm of the lever, and the point A is the line of action of the force F. , B is the vertical line BD of AC and D is the foot pedal, then BD is the power arm. According to the balance condition of the lever, F·BD=G·