表面张力是液体与气体接触的液体表面起到薄弹性片的作用的现象。该术语通常仅在液体表面与气体(例如空气)接触时使用。如果表面位于两种液体(如水和油)之间,则称为“界面张力”。各种分子间力,例如范德瓦尔斯力,将液体颗粒吸引在一起。沿着表面,颗粒被拉向剩余的液体,如右图所示。表面张力(用希腊变量γ表示)定义为表面力F与力作用的长度d的比率:γ= F / d表面张力的单位表面张力以SI单位N / m测量(牛顿每米),虽然更常见的单位是cgs单位dyn / cm(达因/厘米)。为了考虑情况的热力学,有时根据每单位面积的工作来考虑它。在这种情况下,SI单位是J / m2(每平方英寸焦耳)。 cgs单位是erg / cm2。这些力将表面颗粒结合在一起。虽然这种结合很弱 – 毕竟它很容易打破液体表面 – 它确实在很多方面表现出来。滴水。当使用水滴管时,水不会以连续流的形式流动,而是以一系列液滴流动。液滴的形状由水的表面张力引起。水滴不是完全球形的唯一原因是由于重力拉下它。在没有重力的情况下,液滴将使表面积最小化以使张力最小化,这将导致完美的球形形状。走在水的昆虫。几种昆虫能够在水上行走,例如水str。它们的腿形成为分散它们的重量,使液体表面变得凹陷,使潜在的能量最小化以产生力的平衡,使得str脚可以在不破坏表面的情况下穿过水面移动。这在概念上类似于穿着雪鞋在没有脚下沉的情况下穿过深雪堆。针(或纸夹)漂浮在水面上。即使这些物体的密度大于水,沿着凹陷的表面张力也足以抵消向下拉动金属物体的重力。单击右侧的图片,然后单击“下一步”,查看此情况的力图或自行尝试浮针技巧。当你吹肥皂泡时,你会产生一个加压的空气泡,它包含在薄薄的弹性液体表面内。大多数液体不能保持稳定的表面张力以产生气泡,这就是为什么在这个过程中通常使用肥皂……它通过称为Marangoni效应的东西来稳定表面张力。 当气泡吹胀时,表面膜趋于收缩。这导致气泡内的压力增加。气泡的大小稳定在气泡内的气体不会进一步收缩的尺寸,至少不会使气泡爆裂。事实上,肥皂泡上有两个液 – 气界面 – 泡泡内侧的一个和气泡外侧的一个。在两个表面之间是薄膜液体。肥皂泡的球形形状是由表面积的最小化引起的 – 对于给定体积,球体总是具有最小表面积的形式

美国加州理工大学物理学Essay代写:表面张力

Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas, acts like a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air). If the surface is between two liquids (such as water and oil), it is called “interface tension.” Various intermolecular forces, such as Van der Waals forces, draw the liquid particles together. Along the surface, the particles are pulled toward the rest of the liquid, as shown in the picture to the right. Surface tension (denoted with the Greek variable gamma) is defined as the ratio of the surface force F to the length d along which the force acts: gamma = F / d Units of Surface Tension Surface tension is measured in SI units of N/m (newton per meter), although the more common unit is the cgs unit dyn/cm (dyne per centimeter). In order to consider the thermodynamics of the situation, it is sometimes useful to consider it in terms of work per unit area. The SI unit, in that case, is the J/m2 (joules per meter squared). The cgs unit is erg/cm2. These forces bind the surface particles together. Though this binding is weak – it’s pretty easy to break the surface of a liquid after all – it does manifest in many ways. Drops of water. When using a water dropper, the water does not flow in a continuous stream, but rather in a series of drops. The shape of the drops is caused by the surface tension of the water. The only reason the drop of water isn’t completely spherical is because of the force of gravity pulling down on it. In the absence of gravity, the drop would minimize the surface area in order to minimize tension, which would result in a perfectly spherical shape. Insects walking on water. Several insects are able to walk on water, such as the water strider. Their legs are formed to distribute their weight, causing the surface of the liquid to become depressed, minimizing the potential energy to create a balance of forces so that the strider can move across the surface of the water without breaking through the surface. This is similar in concept to wearing snowshoes to walk across deep snowdrifts without your feet sinking. Needle (or paper clip) floating on water. Even though the density of these objects is greater than water, the surface tension along the depression is enough to counteract the force of gravity pulling down on the metal object. Click on the picture to the right, then click “Next,” to view a force diagram of this situation or try out the Floating Needle trick for yourself. When you blow a soap bubble, you are creating a pressurized bubble of air which is contained within a thin, elastic surface of liquid. Most liquids cannot maintain a stable surface tension to create a bubble, which is why soap is generally used in the process … it stabilizes the surface tension through something called the Marangoni effect.

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