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Surface tension is the cohesive force of liquid molecules that allows resistance to external forces. It arises from attraction between molecules, causing a net force of zero within the liquid. Surface tension creates water droplets and bubbles, and is harnessed by some animals. It is measured in dyne per centimeter, which is the force required to break the surface over one centimeter.
Surface tension is the cohesive force exhibited by the molecules of a liquid. This force allows the surface of a liquid to resist, to some extent, external forces applied to it. It is this resistance that allows, for example, a paper clip to float on the surface of a glass of water even though the paper clip has a higher density than water. The voltage varies, depending on the liquid, and with other factors such as temperature.
The tendency of a liquid to exhibit the property of surface tension arises from the attraction that the molecules of a liquid have for each other. Within the liquid, each molecule is surrounded by other molecules, and each molecule attracts every other surrounding molecule equally, resulting in a net force of zero. The molecules on the surface of the liquid, however, are not surrounded in all directions by other molecules. They pull harder on the molecules that are close to them, creating surface tension.
Water droplets form due to surface tension and it also allows air to form bubbles in a liquid. When molecules on the surface of a liquid attract other molecules on the surface, a volume of liquid in space will tend to form a sphere, and in the absence of gravity, water droplets will form perfect spheres. This occurs because a sphere is the shape that has the smallest possible surface area for a given volume. When two small droplets collide in weightlessness, the attraction of molecules to other molecules tends to cause the droplets to combine into a larger droplet. This trend can sometimes be observed even under standard Earth gravity conditions.
The elongated shape of raindrops is due to the force of gravity on the drops. Surface tension tends to be a very weak force, so droplets are easily deformed by gravity or other forces such as centripetal or centrifugal forces. Some insects and even animals have adapted to harness this force, however weak it may be. Aquatic insects and small lizards called basilisks actually rely on the surface tension of water to walk on it without sinking.
The surface tension of a liquid, usually expressed as dyne per centimeter, is the amount of force required to break the surface of a particular liquid over a linear distance of one centimeter. A dyne is a unit of energy or force defined as the amount of energy required to accelerate one gram of mass at the rate of one centimeter per second squared. A dyne is also equal to the International Standard (SI) unit of the micro-newton.
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