What happens to the viscosity of a fluid as the temperature increases?

As the temperature of a fluid increases, its viscosity generally decreases. Viscosity is a measure of a fluid's resistance to flow; it reflects how thick or sticky a fluid is. When the temperature rises, the molecules in the fluid gain energy and move more freely, which reduces the fluid's internal friction and allows it to flow more easily. This phenomenon is observed in many liquids, including common lubricants, where elevated temperatures lead to lower viscosity readings.

For example, consider oil in an engine: when the engine heats up during operation, the oil becomes less viscous, allowing it to better penetrate and lubricate the components, which helps reduce wear and maintain efficiency. Understanding this relationship is crucial for machinery lubrication, as it influences the performance and protection provided by lubricating oils at varying operating temperatures.