As gas temperature increases, viscosity increases. The effect of temperature on viscosity is the opposite for gases. Temperature increases in a liquid decreases viscosity because it gives molecules enough energy to overcome intermolecular attraction. Temperature, however, has the greatest impact on viscosity. Sugar, for example, makes water more viscous. Adding molecules can have a significant effect. Pressure has a small effect on liquids and is often ignored. Examples include temperature, pressure, and the addition of other molecules. A fluid with a low viscosity is said to be “thin,” while a high viscosity fluid is said to be “thick.” It is easier to move through a low-viscosity fluid (like water) than a high-viscosity fluid (like honey). When we fill the same cup with water, for example, the water will drain much more quickly. This is because honey’s viscosity is relatively high when compared to other liquids. I notice that the cup drains very slowly when we pour honey into it. Consider a cup made of styrofoam with a hole at the bottom. The best way to visualize this is through an example. Just like in the case of friction between moving solids, viscosity will determine the energy required to make a fluid flow. This can also be considered to be friction between the molecules. On a molecular level, viscosity is caused by the interactions between different molecules in a fluid. Fluids with low viscosity flow easily because their molecular makeup creates little friction when they are in motion. Viscous fluids resist motion because their molecular makeup creates a lot of internal friction. A fluid’s viscosity is a measure of its resistance to flow. It describes the internal friction of a moving fluid.

Best liquids to test heat and viscosity