The property of a liquid’s surface that allows it to resist an external force due to the cohesive nature of its molecules is known as surface tension. Surface tension is caused by electrostatic forces between liquid molecules that work to reduce the liquid’s surface area. Surface tension is made clear, for example, by the ability of some objects to float on the surface of water despite being denser than water. Some insects, such as water striders, and even reptiles, such as basilisks, can run on the water’s surface due to surface tension.
Surface Tension Formula
Surface Tension Unit
The surface tension unit, when measured in SI units, is N/m (newton per meter), although the more common unit is the cgs unit Dyne/cm (dyne per centimeter).
Considering the thermodynamics of the situation, it is sometimes useful to consider it in terms of work per unit area. The Surface tension unit, in that case, is the J/m2 (joules per meter squared). The cgs unit is erg/cm2.
Surface Tension Definition
Surface tension is a phenomenon in which the surface of a liquid acts as a thin elastic sheet when it comes into contact with a gas. This term is typically used only when the liquid surface is in contact with gas (such as the air). The surface tension between two liquids (such as water and oil) is referred to as “interface tension.”
The Surface Tension of Water
The surface tension of water is caused by water molecules attracting one another as each molecule forms a bond with the molecules around it. As the surface layer of molecules has fewer molecules to cling to, it compensates by forming stronger bonds with its neighbors, resulting in the formation of surface tension.
The surface tension of water is 0.07275 joule per square meter. Organic liquids, such as benzene and alcohol, have lower surface tensions than mercury, which has higher surface tension.
Surface Tension Dimensional formula
The surface tension dimensional formula goes as follows:
Surface Tension Examples
- Shape of liquid droplets: Droplets of water are drawn into a spherical shape by the surface layer’s cohesive forces.
- Spherical shape of bubbles: Water’s surface tension provides the necessary wall tension for the formation of bubbles. The tendency to reduce wall tension causes the bubbles to form spherical shapes.
- Easy to wash clothes in hot water: The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent.
- Test for jaundice: The surface tension of normal urine is about 66 dynes/centimeter, but if bile is present (a test for jaundice), it drops to about 55. Powdered sulfur is sprinkled on the urine surface during the Hay test. It floats in normal urine but sinks when the surface tension is reduced by the bile.
- Walking on water: Water striders and other small insects can walk on water because their weight is insufficient to penetrate the surface.
- Floating needle: Small needle can be made to float on the surface of the water even though it is several times as dense as water, this is because of the surface tension.
- Disinfectants: Disinfectants are typically low surface tension solutions. This allows them to spread out and disrupt bacterial cell walls.
- Soaps and detergents: Soaps and detergents aid in the cleaning of clothes by lowering the surface tension of the water, allowing it to more easily penetrate pores and soiled areas.
Surface Tension – FAQs
Q1. What is Surface tension?
Ans. Surface tension is a property of a liquid that makes it behave as if its surface is enclosed in an elastic skin. The intermolecular cohesive forces among the molecules are responsible for this property.
Q2. Why it is easier to wash clothes in hot water?
Ans. The surface tension between the water and dirt molecules makes it difficult to remove dirt from clothes. To completely and effectively remove dirt, we must reduce the surface tension of the water. As the surface tension decreases with increasing temperature in liquids, it becomes easier to wash clothes in hot water (because its surface tension is low).
Q3. What is the SI unit of the surface tension?
Ans. Surface tension unit: SI unit- N/m (newton per meter)