The difference between materials with high and low viscosity is their thickness. Low viscosity substances, such as water, are thin, whereas high viscosity substances are thick. Syrup is an example of a liquid with a high viscosity.
In addition to assessing thickness, viscosity also measures motion resistance. For instance, a substance with a high viscosity opposes movement, whereas a substance with a low viscosity travels swiftly. Therefore, viscosity measures the internal friction caused by the movement of a substance’s molecular structure. Viscosity is most commonly evaluated on liquids; nevertheless, some gases have detectable viscosity that is not visible to the naked eye.