Solids, Liquids, Gases, and Plasmas


Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure .

Each bottle contains the same volume of oil. How would you describe the shape of the oil in each bottle?

Two interesting properties of liquids are surface tension and viscosity.

  • Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like those in Figure.
  • Viscosity is a liquid’s resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure is more viscous than the vinegar.

These images illustrate surface tension and viscosity of liquids.

You can learn more about surface tension and viscosity at these URLs: