如图所示，用弹簧测力计拉着物体在水平面上向右匀速运动，该物体受到的摩擦力为______N，方向是______；现用4.2N的拉力水平向右拉物体，该物体受到的摩擦力为______N．
（1）由图可知，弹簧测力计分度值是0.2N，示数是3.6N，即物体所受拉力是3.6N，由于物体做匀速直线运动，所以拉力与摩擦力是一对平衡力，所以摩擦力是3.6N，方向水平向左；
（2）当用4.2N的拉力水平向右拉物体时，物体对接触面的压力和接触面的粗糙程度都没有变，所以摩擦力不变，仍为3.6N．
故答案为：3.6；水平向左；3.6．
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| The amount of usable water has always been of great interest in the world. 1 springs and streams sometimes means control, particularly in the 2 areas like the desert. The control is possible even without possession of large areas of 3 land. In the early days of the American West, gun fights were not 4 for the water resources (资源). And laws had to be 5 to protect the water rights of the 6 and the use of the water resources accordingly. 7 is known to us all, there is not 8 water in all places for everyone to use as much as he likes. Deciding on the 9 of water that will be used in any particular period 10 careful planning, so that people can manage and use water more 11 . Farmers have to change their use of or demand for water 12 the water supply forecast (预报). The 13 water supply forecast is based more on the water from the 14 than from the below. Interest is 15 in the ways to increase rainfall by man-made methods, and to get water from the winter snow on mountain 16 . With special equipment, some scientists are studying the ways in which the mountain snow can be 17 , and with the help of a repeater station, they send the 18 data (数据) to the base station. The operator at the base station can get the data at any time by 19 a button. In the near future, the forecast and use of water 20 probably depend on the advance knowledge of snow on mountains, not of water underground. | ||||
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