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A liquid is a state of matter that has a definite size or volume but not a definite shape. A liquid takes the shape of the container in which it is held and presses on the container in the same amount in all directions. The molecules in a liquid are closer together than those in a gas but not as close together as those in a solid. The molecules in solids are in a fixed position but those in liquids move around more.

Although molecules in a liquid hang together through forces called cohesion, The molecules at the surface of a liquid can also jump off from the liquid into the surrounding air in a process called evaporation. The rate of evaporation depends on the humidity of the air, how much of the surface of a liquid is exposed to the air, and the temperature.

Most liquids expand or spread out when heated and contract when cooled. When a liquid is heated to its boiling point, it changes to a gas. When a liquid is cooled to its freezing point, it becomes a solid. The melting point and boiling point are two ways to tell what a liquid is as liquids can differ in these measures. Heating a mixture can be used to separate out the parts of a mixture.

One property of liquids is diffusion. Diffusion is when the movement of a concentration in one part of a liquid that is higher to a part of the substance where the concentration is lower.

Liquids are also difficult if not impossible to compress.

Liquids also exert buoyancy on other objects placed within the liquid. The amount of buoyancy is equal to the amount of the liquid that is pushed out of place when the object is placed in the liquid.

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