分子间的作用力

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分子间有空隙

生活中我们会发现,气体很容易被压缩;水和酒精混合后,总体积会变小;压在一起比较久的铁和铝,可以互相进入对方,等等的这些生活列子,都说明了分子间有空隙。

分子间的相互作用

分子之间虽然有空隙,但大量的分子却可以聚在一起形成固体或液体,说明分子间存在引力(如用力拉伸物体,物体会产生反抗拉伸的弹力);但用力压缩物体,物体内会产生反抗压缩的弹力,这说明了分子之间还存在着斥力。

研究表明,两个相邻的分子之间同时存在着引力和斥力,某些情况下分子之间表现为引力,某些情况下分子之间表现为斥力,并且引力和斥力的大小都跟分子间的距离有关,关系如下:

分子之间作用力和距离的关系

分子间的引力、斥力、分子力(引力与斥力的合力叫做分子力)与距离之间的变化关系。

分子之间作用力的特点:

1、分子引力和斥力都随分子间距离的增大而减小,随距离的减小而增大,分子间的作用力属于电磁力。

2、当分子间距离变化时,分子斥力比引力变化的快。

(1)当rro=10-10m时,F引<F斥,分子力表现为斥力。

(2)当rro时,F引=F斥,分子力为0。

(3)当rro时,F引>F斥,分子力表现为引力。

(4)当r>10ro时,F引→0,F斥→0,分子力为零。

分子之间的作用力的合力很像用弹簧连接的两个小球之间的作用力:当弹簧长度大于原长(伸长)时,表现为引力;当弹簧长度小于原长(压缩)时,表现为斥力。

分子动理论

1、分子动理论的内容:物体是由大量分子组成,分子在做永不停息的无规则运动,分子之间存在着引力和斥力。

2、分子运动的统计规律:大量偶然事件的整体所表现出来的规律叫做统计规律。因为分子的热运动是无规则的,所以对任何一个分子来说,它的运动情况具有偶然性,不可预测,但对于大量分子的整体而言,它们却表现出规律性。


高中物理知识点总结

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