Viscous fluids are substances that resist flow due to internal friction. This resistance is known as viscosity, which measures how thick or sticky a fluid is. For example, honey has a higher viscosity than water, making it flow more slowly. Viscosity can change with temperature; heating a fluid often reduces its viscosity, allowing it to flow more easily. Common examples of viscous fluids include oils, glycerin, and molasses. In engineering and science, understanding the viscosity of fluids is crucial for applications like lubrication, fluid transport, and chemical processing. The behavior of viscous fluids is essential in fields such as mechanical engineering and fluid dynamics.