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误解一同一个杠杆只有一个支点例1如图1所示,用一根硬棒撬块石头,棒的上端A是动力的作用点。在图中标出:当动力的方向向上时,杠杆的支点a;当动力的方向向下时,杠杆的支点b。错解无论是动力的方向向上还是向下,杠杆的支点都有是硬棒与地的接触点,即a点。正解当动力的方向向上时,如图2所示,硬棒与地的接触点a为此时的支点,杠杆绕支点头a使石头转动;当动力的方向向下时,如图3所示,硬棒与小石头的接触点b为此时的支点,杠杆绕支点b使石头转动。
Misunderstanding of the same lever with only one fulcrum Example 1 As shown in Figure 1, a hard stick is used to smash the stone, and the upper end of the stick A is the point of power. Marked in the figure: when the direction of power is upward, the fulcrum a of the lever; when the direction of power is downward, the fulcrum b of the lever. Whether the direction of power is up or down, the fulcrum of the lever has a point of contact between the hard rod and the ground, ie a point. Positive solution When the direction of power is upward, as shown in Fig. 2, the contact point a between the hard bar and the ground is the fulcrum at this time. The lever rotates the stone around the fulcrum head a; when the direction of power is downward, as shown in FIG. 3. The contact point b between the hard rod and the small stone is the fulcrum at this time, and the lever rotates the stone around the pivot point b.