Have you ever seen tiny insects, such as water striders, moving over a pond’s surface without sinking? Have you ever observed how water doesn’t spread out on smooth leaves but instead of this creates droplets? Surface tension is a characteristic of liquids that causes these interesting events.
What is Surface Tension?
The tendency of a liquid surface to act like a stretched elastic sheet is known as surface tension. It results from the cohesive (attractive) forces that exist between the liquid’s molecules.
To put it simple, surface tension is the characteristic that causes a liquid’s surface to behave as wrapped in an invisible skin. This explains why, despite being denser than water, small objects like needles can occasionally float on it.
Why Does Surface Tension Occur?
Following are the facts on that basis we can examine molecular processes.
Within the Liquid: The majority of a liquid’s molecules are subject to equal attractive forces from their nearby molecules in all directions. They remain stable because of this balancing force.
At the Surface: Because there are no molecules above them, molecules at the surface feel a net inward push. The surface contracts as a result of this inward force, acting like a stretched membrane. Because a sphere has the smallest surface area for a given volume, this effect causes the liquid to try to decrease its surface area, which results in the creation of spherical droplets.
Surface Tension Formula and Unit
The surface tension (γ) of a liquid is defined as the force per unit length acting on the surface of the liquid. It is given by the formula: γ = F / L
Where:
γ = Surface tension (N/m)
F = Force acting along the surface (N)
L = Length along which the force acts (m)
The SI unit of surface tension is Newton per meter (N/m).
Examples of Surface Tension in Daily Life
Water Droplets on a Surface: When water falls on a surface, it creates droplets. The reason for this is that molecules are drawn together by surface tension to create a shape with a small surface area.
Soap Bubbles: By lowering the water’s surface tension, soap facilitates the blowing of bubbles. The forces operating on the surface cause the bubble to create a thin layer.
Floating Needle: Despite the fact that metal is denser than water, a needle can remain afloat if it is precisely positioned on the water’s surface because of surface tension.
Insects Walking on Water: Certain insects, such as water striders, can walk on water without sinking by using surface tension. They avoid shattering the surface because their legs disperse their weight over a wide region.
Capillary Action: Surface tension causes the liquid in a narrow tube to rise when it is submerged in water. For this reason, plants can use their roots to draw water from the soil.
How Surface Tension Changes with Temperature?
As the temperature rises, surface tension falls. This occurs as a result of the molecules’ increased kinetic energy at higher temperatures, which weakens their cohesive forces. Liquids consequently become less “sticky” at higher temperatures.
Effects of Surface Tension in Nature and Industry
Raindrops are spherical because the water molecules are drawn together by surface tension to create the smallest surface area possible.
• Using detergents to clean: Detergents and soaps lower the surface tension of water, which facilitates spreading and surface cleaning.
• Medical Applications: A chemical known as a surfactant lowers the fluids’ surface tension in the human lungs, facilitating better breathing.
Summary
A vital characteristic of liquids that influences many commercial and natural processes is called surface tension. Droplets develop, objects float on water, and even the way we clean with soap are all caused by it.
The characteristic of a liquid surface that causes it to act like a stretched elastic sheet is called surface tension. The surface minimises its area as a result of the cohesive forces between liquid molecules.
The formula for surface tension is:
γ = F / L
where γ (gammaγ) is surface tension, F is force, and L is length.
Its SI unit is Newton per meter (N/m).
Droplets of water developing on a surface.
Water striders are insects that walk on water.
A spherical shape formed by soap bubbles.
When we gently positioned, a needle on water’s surface its floats.