Shop Windows to the Universe

Become a nitrogen atom in the nitrogen cycle in our Traveling Nitrogen Classroom Activity Kit/Game. See all our games, activity kits and classroom activities.
Milk is a typical liquid. A liquid takes on the shape of the container it is in; in this case a glass. Liquids have a distinct boundary called a "free surface"; in this case, near the top of the glass where the milk meets the air above it.
Click on image for full size
Image courtesy of Corel Corporation.

Liquids

Liquid is one of the four common states of matter. The three others are gas, solid, and plasma. There are also some other exotic states of matter that have been discovered in recent years.

A liquid does not have a fixed shape, like a solid; instead it takes on the shape of the container that it is in. Liquids can flow. A liquid has a distinct surface, unlike a gas. This surface is called a free surface. For example, water in a glass has a surface where the water ends and the air above it begins.

When a liquid boils or evaporates, it becomes a gas. When a liquid freezes, it becomes a solid. For example, when liquid water boils, it becomes water vapor. When liquid water freezes, it becomes ice.

In everyday life we think of a liquid and a fluid as being the same thing. Scientists use the term "fluid" in a special way, though, to mean things that can flow. Liquids, gases, and plasmas are all fluids as far as scientists are concerned.

Water is probably what you think of when someone mentions a liquid. Milk, gasoline, and cooking oil are other common liquids. Some common substances, like the oxygen and nitrogen in air, are gases under "normal" circumstances but can become liquids if they are very, very cold. Mercury is a kind of metal that is a liquid at normal temperatures; it doesn't "freeze" and become a solid until cooled to -39 C (-38 F). Glass and steel become liquids when they are heated to very, very high temperatures.

Last modified June 25, 2008 by Randy Russell.

Shop Windows to the Universe Science Store!

Our online store includes fun classroom activities for you and your students. Issues of NESTA's quarterly journal, The Earth Scientist are also full of classroom activities on different topics in Earth and space science!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Solid

Solid is one of the four common states of matter. The three others are gas, liquid, and plasma. There are also some other exotic states of matter that have been discovered in recent years. Unlike liquids...more

The Plasma State

Plasma is known as the fourth state of matter (the first three states being solid, liquid and gas).Matter in ordinary conditions on Earth has electrons that orbit around the atomic nucleus. The electrons...more

Changes of State: Solids, Liquids, and Gases

Any substance, called matter, can exist as a solid material, liquid, or gas. These three different forms are called states. Matter can change its state when heated. As a solid, matter has a fixed volume...more

Evaporation

One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on factors...more

The Cryosphere

The cryosphere includes the parts of the Earth system where water is in its frozen (solid) form. This includes snow, sea ice, icebergs, ice shelves, glaciers, ice sheets, and permafrost soils. Approximately...more

Oxygen

Oxygen is a chemical element with an atomic number of 8 (it has eight protons in its nucleus). Oxygen forms a chemical compound (O2) of two atoms which is a colorless gas at normal temperatures and pressures....more

Nitrogen

Nitrogen is a chemical element with an atomic number of 7 (it has seven protons in its nucleus). Molecular nitrogen (N2) is a very common chemical compound in which two nitrogen atoms are tightly bound...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA