Surface tension is a cohesive force exhibited by liquid molecules that allows the surface of the liquid to resist externally applied forces and maintain a minimized surface area. This is why water droplets can gather on the leaves and insects can slip over the pond. Attracted by how this unseen force shapes our world? Let's explore the mystery of surface tension and its impact on everyday life.
Surface tension is produced by the cohesive force between the molecules of a liquid. This force makes the surface of the liquid resistant to the force exerted by the outside world to a certain extent. It is this resistance that allows a paper clip, for example, to float on the surface of a glass of water, even if the density of the paper clip is greater than that of water. The magnitude of the surface tension depends on the type of liquid, as well as other factors such as temperature.
The tendency of liquids to exhibit surface tension is because of the mutual attraction between the molecules of the liquid. Inside the liquid, each molecule is surrounded by other molecules around it, and each molecule has the same attraction towards every other molecule around it, resulting in a zero net force. However, the molecules on the surface of the liquid are not surrounded by other molecules in all directions. They exert a stronger force of attraction on the molecules in their vicinity, creating surface tension.
Water droplet formation is due to surface tension, and it also allows air to form bubbles in the liquid. As the molecules on the surface of the liquid exert traction on other molecules, the volume of liquid in one space tends to form a sphere, whereas in the absence of gravity, the water droplets form a perfect sphere. This is because a sphere is the shape with the smallest surface area for a given volume. When two small water droplets collide without gravity, the attraction of the molecules to the other molecules makes them tend to combine into one larger water droplet. This trend can also sometimes be observed under standard Earth gravity.
The extended shape of the raindrops is due to the pull force of gravity on the water droplets. Surface tension tends to be a very weak force, so water droplets can easily be deformed by gravity or other forces such as centripetal or centrifugal forces. However, some insects and even animals have adapted to harness this power, although it may be weak. Water bugs and a small lizard called a "walking dragon" actually rely on the surface tension of water to walk on the surface of the water without sinking.
The surface tension of a liquid is usually expressed in dynes per centimeter, which indicates the force required to break the surface of a certain liquid at a linear distance of one centimeter. A Davy is defined as the unit of energy or force required to accelerate a gram mass at a rate of square centimeters per second. One Davy is also equal to Webull's International Standard (SI) unit.