拉力常用F表示。在弹性限度以内,物体受外力的作用而产生的形变与所受的外力成正比。形变随力作用的方向不同而异,使物体延伸的力称“拉力”或“张力”。(推力、拉力、提力、压力、浮力统称为:拉力)
拉力是按力的效果定义的,从力的性质来看,拉力也是弹力,而从力的作用对象来看,拉力可能是内力,也可能是外力。
如果物体在受到阻力和拉力两个力的情况下,如果物体做匀速直线运动或保持静止状态,那么此时F拉=F阻,拉力和阻力是一对平衡力,物体处于二力平衡状态(合力为零)。在特定情况下,如果物体做加速运动,则F拉>F阻;如果物体做减速运动,则F拉<F阻。
汽车作匀速直线运动时,拉力(牵引力)跟摩擦力平衡。
拉力简写为F,力的单位为牛顿,简称牛,符号N。
拉力公式:f=w/s
弹簧的拉力大小F跟弹簧的伸长(或缩短)的长度成正比,即F=kx
式中的k叫做弹簧的劲度系数,其大小取决于弹簧本身,k的单位是N/m。这就是胡克定律。
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