滑轮,一般有两种:一种是定滑轮,用这种滑轮不能省力,但是可以改变力的方向;另一种是动滑轮,使用它来提起重物,可以省一半的力,但是没有改变力的方向的作用。在教学中,这些都可以用实验来证明,只要注意减少摩擦力的影响,实验的结的果一般是比較准确的。除了实验,还可以讲些浅显的道理。两种滑轮,实际上都是杠杆的变形。定滑轮是支点在中间的一种杠杆,转軸就是支点,它的力点在滑轮的一边,离开支点的距离,等于滑轮的半径,重点在滑轮的另一边,离支点的距离也等于滑轮的半径。因为力点和重点离支点的距离相等,所以使用它不能省力。但是有改变力的方向的作用,这在許多场合下,可以使我們 There are two kinds of pulleys, one is a fixed pulley, which can not be saved with the help of this pulley, but can change the direction of the force. The other one is a movable pulley, which can be used to lift heavy objects, which can save half the force but no change in force The role of the direction. In teaching, these can be experimentally proved, as long as the attention to reduce the impact of friction, the results of the experiment is generally more accurate. In addition to experiments, you can also make some plain truths. Two kinds of pulleys, are actually the deformation of the lever. The fixed pulley is the fulcrum in the middle of a lever, shaft is the fulcrum, its force point in the pulley side, the distance from the fulcrum, equal to the radius of the pulley, focusing on the other side of the pulley, the distance from the fulcrum is equal to the radius of the pulley . Because the force point and the focus from the fulcrum distance equal, so it can not be used to save effort. But the role of change direction, which on many occasions can make us