Q： 什么是表面張力？

A：液(ye)(ye)(ye)體(ti)(ti),原來液(ye)(ye)(ye)體(ti)(ti)與(yu)氣體(ti)(ti)相接(jie)觸時，會形(xing)成一個表(biao)(biao)面(mian)(mian)層(ceng)(ceng)，在(zai)這個表(biao)(biao)面(mian)(mian)層(ceng)(ceng)內(nei)存在(zai)著的(de)相互吸引力就是表(biao)(biao)面(mian)(mian)張力，它能(neng)(neng)(neng)(neng)使液(ye)(ye)(ye)面(mian)(mian)自動收縮。表(biao)(biao)面(mian)(mian)張力是由液(ye)(ye)(ye)體(ti)(ti)分子(zi)間(jian)(jian)很大的(de)內(nei)聚力引起(qi)的(de).不(bu)(bu)(bu)光液(ye)(ye)(ye)體(ti)(ti)與(yu)氣體(ti)(ti)之間(jian)(jian)的(de)表(biao)(biao)面(mian)(mian)層(ceng)(ceng)，液(ye)(ye)(ye)體(ti)(ti)與(yu)固體(ti)(ti)器(qi)壁之間(jian)(jian)也存在(zai)著“表(biao)(biao)面(mian)(mian)層(ceng)(ceng)”，這一液(ye)(ye)(ye)體(ti)(ti)薄層(ceng)(ceng)通(tong)常叫做附著層(ceng)(ceng)，它也一樣存在(zai)著表(biao)(biao)面(mian)(mian)張力。這一表(biao)(biao)面(mian)(mian)張力決定(ding)了液(ye)(ye)(ye)體(ti)(ti)和(he)固體(ti)(ti)接(jie)觸時，會出(chu)現(xian)兩種(zhong)(zhong)現(xian)象：不(bu)(bu)(bu)浸(jin)潤(run)(run)和(he)浸(jin)潤(run)(run)現(xian)象。水(shui)(shui)銀(yin)(yin)掉到玻(bo)(bo)璃(li)上(shang)，是呈現(xian)出(chu)球形(xing)，也就是說，水(shui)(shui)銀(yin)(yin)與(yu)玻(bo)(bo)璃(li)的(de)接(jie)觸面(mian)(mian)具有收縮趨勢，這種(zhong)(zhong)現(xian)象為不(bu)(bu)(bu)浸(jin)潤(run)(run)。而(er)水(shui)(shui)滴(di)掉到玻(bo)(bo)璃(li)上(shang)，是慢(man)慢(man)地沿(yan)玻(bo)(bo)璃(li)散(san)開，接(jie)觸面(mian)(mian)有擴大趨勢，這種(zhong)(zhong)現(xian)象為浸(jin)潤(run)(run)。水(shui)(shui)銀(yin)(yin)雖(sui)然不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)玻(bo)(bo)璃(li)，但是用稀(xi)硫酸把鋅板(ban)擦干凈(jing)后，再在(zai)板(ban)上(shang)滴(di)上(shang)水(shui)(shui)銀(yin)(yin)，我(wo)們將會看到，水(shui)(shui)銀(yin)(yin)慢(man)慢(man)地沿(yan)鋅板(ban)散(san)開，而(er)不(bu)(bu)(bu)再呈球形(xing)。所(suo)以說，同一種(zhong)(zhong)液(ye)(ye)(ye)體(ti)(ti)能(neng)(neng)(neng)(neng)夠浸(jin)潤(run)(run)某(mou)些固體(ti)(ti)，而(er)不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)另一些固體(ti)(ti)。水(shui)(shui)銀(yin)(yin)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)鋅，而(er)不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)玻(bo)(bo)璃(li)；水(shui)(shui)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)玻(bo)(bo)璃(li)，而(er)不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)浸(jin)潤(run)(run)石蠟。