丁—chapter 5 liquid surface课件.ppt

The properties of a liquid ,especially its surface ,are of paramount importance to the biologist and medical scientist . The surface properties of a liquid arise from the interactions among liquid molecules ,and the interactions among the molecules of liquid and those of other substances .In this chapter ,we will discuss some important surface properties of liquid ,which including the surface energy and surface tension ;the additional pressure across a curved surface of a liquid ;the capillarity and some surface tension phenomena on medicine and biology .;To master: ;Section 1 surface energy and surface tension;surface properties;;顷漏巨崩撂沿炬逼帛葱氧彭词廊株淮振蛇镍施切嗣巷跌绒休斧柒罐嘱冠巨丁—chapter 5 liquid surface课件丁—chapter 5 liquid surface课件;The surface behaves ,in fact ,as if it were a stretched rubber sheet that constantly tried to decrease its area . There is ,therefore ,a tension acting on a cross any imaginary line drawn in the surface . It proves that surface of liquid has tension (张力). It is called surface tension (表面张力).; If we divide a liquid surface into two sides by an imaginary line drawn in the surface ,The material on either side of the line exerts a pull ,or the surface tension ,lies in (or tangent to )the surface ,and is perpendicular to the line . Its magnitude is proportional to the length of the line l; f = ? l;coefficient of surface tension ;Question: Surface tension(产生,液面为何收缩) It is known that the equivalent (平衡的) distance between two molecules is denoted by r0 which is about 10-10 m in length. Generally speaking, when the distance between two molecules, denoted by d, is less than r0, the force between the two molecules is repulsion (斥力) and when the distance between two molecules;is larger than r0, the force between them should be gravitation (引力). However, when d 10-9m, the gravitation between two molecules can be taken as zero. Only if a molecule is in the sphere of radius of 10-9 m, it can be gravitated by the center of molecule. This