The bucket containing more water has more mass. Ask the student volunteer which bucket appears to have more mass.Select a student to lift both buckets of water.Half-fill one bucket and add only about 1 cup of water to the other.Two identical buckets or large containers.Students will be able to explain that since any volume of water always has the same density, at a given temperature, that density is a characteristic property of water. Students will be able to measure the volume and mass of water and calculate its density. Students make a graph of the relationship between the volume and the mass of water. Then they measure the mass of different volumes of water and discover that the density is always the same. Students measure the volume and mass of water to determine its density. The density of a substance is the same regardless of the size of the sample.The density of water is 1 gram per cubic centimeter.Just like a solid, the density of a liquid equals the mass of the liquid divided by its volume D = m/v.The mass and size of the molecules in a liquid and how closely they are packed together determine the density of the liquid. The molecules of different liquids have different size and mass. The volume of a liquid can be measured directly with a graduated cylinder.Just like solids, liquids also have their own characteristic density.Plasma will not be discussed in depth in this chapter because plasma has very different properties from the three other common phases of matter, discussed in this chapter, due to the strong electrical forces between the charges. At high temperatures, molecules may disassociate into atoms, and atoms disassociate into electrons (with negative charges) and protons (with positive charges), forming a plasma. There exists one other phase of matter, plasma, which exists at very high temperatures. In this chapter, we generally refer to both gases and liquids simply as fluids, making a distinction between them only when they behave differently. When placed in an open container, gases, unlike liquids, will escape. This makes gases relatively easy to compress and allows them to flow (which makes them fluids). In contrast, atoms in gases are separated by large distances, and the forces between atoms in a gas are therefore very weak, except when the atoms collide with one another. Because the atoms are closely packed, liquids, like solids, resist compression an extremely large force is necessary to change the volume of a liquid. When a liquid is placed in a container with no lid, it remains in the container. That is, liquids flow (so they are a type of fluid), with the molecules held together by mutual attraction. This occurs because the atoms or molecules in a liquid are free to slide about and change neighbors. Liquids deform easily when stressed and do not spring back to their original shape once a force is removed. A gas must be held in a closed container to prevent it from expanding freely and escaping. (c) Atoms in a gas move about freely and are separated by large distances. Forces between the atoms strongly resist attempts to compress the atoms. (b) Atoms in a liquid are also in close contact but can slide over one another. Figure 14.2 (a) Atoms in a solid are always in close contact with neighboring atoms, held in place by forces represented here by springs.
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