The surface tension is mainly related to the density. The density of water is higher than that of oil, so it should be that the surface tension of water is higher than that of oil. Water can form drops on the lotus leaf, but oil cannot. Mercury has a greater density, so Mercury drops on the ground to form mercury beads, but water cannot.
At the boundary between liquid and gas, that is, the surface of the liquid and the interface between two immiscible liquids, due to the attraction between the molecules, a very small pulling force is generated. Imagine that there is a film layer on the surface, which bears the tensile force of the surface. This tensile force of the liquid is called surface tension.
Since the surface tension only exists at the free surface of the liquid or the interface between two liquids that cannot be mixed, the surface tension coefficient σ is generally used to measure its size. σ represents the value of the tensile force per unit length on the surface, in N/m. The surface tension of various liquids covers a wide range, and its value decreases slightly with the increase of temperature.
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In general, the higher the temperature, the lower the surface tension. In addition, impurities will also significantly change the surface tension of the liquid. For example, clean water has a large surface tension, while the surface tension of soapy water is relatively small. That is to say, the surface of clean water has a greater tendency to shrink. .
The mercury drop on the glass plate is basically spherical, because all the molecules in the thin layer on the outer surface of the mercury drop are in a state of high potential energy. Calculations show that if the total potential energy of the molecule is minimized, the surface must be spherical.
Try to eliminate the influence of gravity, such as placing the droplet in another liquid with the same specific gravity but no chemical reaction with the droplet, or falling freely in a vacuum, or in the environment of weightless artificial satellites and rockets. The drop will assume an ideal spherical shape. The spherical soap bubble and the spherical dew on the lotus leaf can also be explained in the same way.