The surface tension

The surface tension of the liquid - a value that accurately characterizes the ability of a liquid to reduce and which is measured by the force of surface tension, have an impact on unit length of the line, on the surface of the liquid.In that case the length dimension of the boundary surface of the liquid is designated as l, and the surface tension of the film, which acts on this edge, - F, so the value of the surface tension will be:

σ = F / l

Name coefficientSurface tension is expressed in N / m.The higher the temperature is, the smaller is the value of σ for clean liquids.

consequence asymmetric molecular interaction forces transition layer with molecules that surround them, is the notion of the existence of normal and tangential forces with respect to the interface.These forces have a significant impact on the molecules of the transition layer.They are the molecular forces of pressure and surface tension between the phases.

Coefficient σ on the presence of various impurities

The surface tension is directly connected with the forces of molecular interaction and can take a variety of values ​​for various liquids.In liquids that evaporate very well (alcohol, benzene, ether), an indicator of surface tension is not as big as in liquids, are not volatile.First put on a grid on a hydrometer and then omit it in the water.Due to the dense grid, the hydrometer will be kept at a certain depth.Followed by dripping a little air on the grid, and then the hydrometer immediately rise out of the water.

The surface tension of water is related to how much impurities in the water.On the surface of the water is put a small splinter from the match.Thereafter, the water descends the soap bar.After a certain period of time can be observed splinter movement to the edge of the vessel from the soap.As a result, one can conclude that the surface tension can be reduced by using soap.If added substances other than the biological activity (toothpaste, soap, detergents), the surface tension will be reduced.Then, if you want to get blisters, why people add soap?

Many of us believe that, thanks to the soap component σ increases.In fact, it just reduces the surface tension component to approximately one-third to one-σ value of pure water.Note that tensile soap film decreases the concentration of soap molecules on the surface, wherein the surface tension increases.Consequently, under the action of the soap bubble amplify weak points and are not expanded further.Moreover, due to soap water evaporates, and thus, the term "life" of the bubble increases.

Now let's put this experience: put sugar candy in water.This will lead to the fact that the splinter will move to the candy.The conclusion is clear: under the influence of sugar component of the surface tension increases.

How to determine the coefficient of σ through the capillaries?

To accomplish this, the simplest of its kind of experience you need to have a few vessels with water and capillaries.

capillary is required to lower in a vessel with water, and then measure the height of liquid rise.Then another capillary tube is placed in soapy water, then measured the height of lifting fluid.The coefficient σ can be found from the corresponding formula:

σ = ρgdh / 4

Then you should compare rates of different types of surface tension of liquids.