Liquids and Density

Scientists use the word “density” to describe the amount of matter in a certain volume. Density is how close together the molecules are in a substance. Liquids are usually less dense than solids but more dense than air.

Temperature can change a liquid’s density. For example, increasing the temperature of water causes the molecules to spread farther apart. The farther apart the molecules are, the less dense the water is.

A solid is usually denser than a liquid, so you might expect an ice cube to sink in water. But instead, it floats. When water freezes into ice, its molecules join together in a special pattern. This pattern has empty space between each molecule, which makes ice less dense than water.

The physical property of density helps scientists separate liquids. When two liquids are placed in a container, the denser liquid will fall to the bottom. The less dense liquid will rise to the top. This is why oil floats above vinegar in a bottle of salad dressing before it is shaken. Vinegar is a sour liquid used in cooking.

A mixture of oil and vinegar will eventually separate. Oil is less dense than vinegar and will float to the top.View Larger Image

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