Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Physical Properties of Liquids

C. Viscosity

The viscosity of a liquid is a measure of how much the liquid resists flow. Flow allows a liquid to take the shape of the container that holds it. A liquid’s viscosity depends on the structure of the liquid’s molecules and on the attractive forces between the liquid’s molecules. Highly viscous liquids often contain molecules that have complicated structures. These molecules can become entangled with one another, impairing their ability to flow past one another. The viscosity of water is lower than that of heavy oils, for example, because oils contain large, convoluted molecules that catch on one another. The polarity of the molecules in water, however, causes them to attract one another, making water more viscous than a nonpolar liquid, such as propane. Viscosity decreases as temperature increases because additional heat energy enables molecules to overcome attractions to one another and move more freely.