March 12, 2013

What is a Liquid?

Hi, my name is Emerald Robinson, and in this “What Is” video, we’re going to investigate the state of matter called a “liquid.”

Liquids are materials that have a definite volume but no specific shape. In other words, liquids can easily flow into and take the shape of the container that they are in, but do not expand to fill that container.

Although types of liquids vary widely, there are a few characteristics that they have in common.

First, particles in a liquid are arranged so that they remain close together. Although the molecules in a liquid can move over and past one another, the space between the molecules remains small. This attraction is called intermolecular bonding.

Second, liquids can’t be compressed. Because there’s not a lot of space between the atoms, they can’t be squeezed together any closer than they already are. Sometimes scientists say that liquids are a “condensed phase” of matter.

Third, they flow from one area to another, generally from a higher to a lower point due to gravity. This ability to flow means they are sometimes called “fluids.”

Last, in general, liquids have melting points at or below room temperature, and boiling points that are higher than room temperature.

Because of the way molecules and atoms are arranged in a liquid, they produce a phenomenon called “surface tension.” Surface tension is the force that causes liquids to form droplets, and to “bead” on surfaces. It even enables very light objects to be borne on the surface of the water, such as in the case of water striders.

Although we’re familiar with and dependent on the most common liquid on earth – water – liquids are actually the rarest form of matter in the universe. This is because liquids can only exist within narrow ranges of temperature and pressure, which are uncommon outside of the earth’s atmosphere.

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