Test: Viscosity - SSC CGL MCQ

Hence, the viscosity of liquids decreases with increase in temperature. For gases, viscosity is due to collision between gas molecules. With increase in temperature, gas molecules attain more kinetic energy and the rate of collision is more. Hence, viscosity of gases increases with increase in temperature.

The SI unit for viscosity is the pascal-second (Pa·s). This unit is commonly used to measure viscosity, representing the resistance to flow in a fluid. It is essential in understanding how fluids behave under different conditions, such as temperature and pressure.

Water at a temperature of 20°C typically exhibits a viscosity of approximately 1 centipoise (cP). This characteristic viscosity value serves as a reference point for understanding the behavior of fluids, especially in applications where water is a common medium.

Viscosity in fluids primarily refers to the fluid's resistance to flow. This property is influenced by factors such as temperature, pressure, and the composition of the fluid. Higher viscosity indicates greater resistance to flow, making it harder for the fluid to move. Understanding viscosity is essential in various scientific fields, including fluid dynamics and materials science.

Viscosity is commonly reported in two ways: dynamic viscosity, which measures a fluid's resistance to flow, and kinematic viscosity, which is the ratio of dynamic viscosity to a fluid's density. Understanding these different ways of measuring viscosity is essential in various fields, including engineering, physics, and chemistry.

At 20 °C, the dynamic viscosity of water is 1.0016 millipascal-seconds (mPa·s). This property indicates how resistant a fluid is to flow under an applied force. Water's viscosity at this temperature is crucial for various applications, from industrial processes to understanding fluid behavior in nature.

Water exhibits a relatively low viscosity compared to most liquids with molecules of similar size because of the presence of hydrogen bonding between water molecules. These intermolecular forces play a significant role in determining the physical properties of water, including its viscosity. The hydrogen bonds create cohesion among water molecules, affecting how easily they can flow past each other.

In accordance with Newton's law of friction, a Newtonian fluid maintains a constant viscosity, independent of the strain rate. This implies that under varying shear rates, a Newtonian fluid's viscosity remains the same.

Bingham plastics behave like solids under regular circumstances but flow as viscous liquids under high stress conditions. This unique characteristic allows them to maintain their structure until a critical stress threshold is reached, beyond which they flow like liquids.

Viscosity is commonly measured using viscometers and rheometers, with rheometers being a specialized type of viscometer. These devices are designed to measure either the flow of a fluid past a stationary object or the movement of an object through a fluid. The viscosity value obtained from these measurements represents the drag between the fluid and the object's surface. An interesting fact is that rheometers are particularly useful in studying complex fluids like gels, pastes, and biological fluids, offering detailed insights into their flow behavior.

The viscosity value obtained from viscometers and rheometers represents the fluid's resistance to flow. This value indicates how easily a fluid flows under an applied force. Higher viscosity values suggest greater resistance, meaning the fluid is more resistant to flowing freely. Understanding viscosity is crucial in various industries, such as food processing, pharmaceuticals, and petroleum, where precise control of flow characteristics is essential for product quality and performance.

In American and British engineering, viscosity is sometimes measured in pound-seconds per square foot (lb·s/ft²). This unit provides an alternate way to quantify viscosity in specific engineering contexts.

When liquids are heated, their viscosity generally decreases because the heat provides the molecules with energy to move more freely past each other. In contrast, heating gases tends to increase viscosity as the molecules collide more frequently, affecting their flow characteristics. This distinction in the behavior of liquids and gases under temperature changes is crucial in understanding their properties and applications.

The viscosity of liquid water decreases significantly as temperature increases from 20 °C to 80 °C. This phenomenon is important in understanding how the fluidity of water changes with temperature variations. The decrease in viscosity has implications for processes like heating water for various purposes, including cooking and industrial applications.

Shear-thinning fluids are characterized by a reduction in viscosity as the shear strain rate increases. This behavior is commonly observed in substances like ketchup, where the fluid becomes less viscous with higher shear rates, facilitating easier pouring or spreading.