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81 2.13. Density An object made of metal is usually much (1) heavier than a wooden one of the same volume. They are both (2) occupying the same amount of space, but the metal object has a greater density. Density is the amount of mass, or atoms, that an object (3) contains in a given space. The metal object contains more tightly (4) packed atoms than the wooden object (5) therefore it has a greater density. 2.14. Kinetic Theory The different (1) behavior of matter in its solid, liquid, and gaseous states is (2) explained by kinetic theory. The state of any particular matter is determined by the (3) amount of energy contained inside its atoms (the (4) tiny particles that make up all matter). Changes of state occur when the energy levels of atoms change. The atoms in a gas have the most energy, those in a solid the least. The (5) total amount of energy contained by the atoms of a substance is known as the kinetic energy of the substance. The substance's temperature and the pressure it is under affect its kinetic energy; so does the (6) volume of its container. 2.15. Blaise Pascal (1623-62) The Frenchman Blasé Pascal was a brilliant mathematician and religious (1) thinker. He was the founder of the modern theory of (2) probability (an expression of the likelihood of something happening). Following work on barometers by Italian scientists Galileo Galilei (1564-1642) and Evangelista Torricelli (1608-47), Pascal made a mercury barometer and (3) measured atmospheric pressure. He formulated Pascal's principle: in a liquid or gas, pressure (4) applied to one point is transmitted (5) equally to all parts of the fluid. He invented the first (6) digital calculator, but it was too costly to make and was never used. 2.16. Pressure You put pressure on something when you (1) apply a force to it. The amount of pressure depends on two things: the size of the force, and, more importantly, the size of the (2) area on which it is applied. The smaller the area, the greater the pressure. This principle (3) explains why thin stiletto heels (4) sink into wooden floors and damage them. It also explains why a camel's large, flat feet (5) prevent it from sinking into the sand in the desert. 2.17. Liquids Liquid is a substance that moves more (1) freely than a solid, but not as freely as a gas. The tiny particles that make up liquids have more energy than those of solids, but not us much as those of gases. Liquids also (2) differ from gases because they cannot be compressed into smaller spaces. The (3) ability of a liquid to resist flowing is called its viscosity. (4) Thick liquids, like syrup, have a high viscosity and flow slowly, whereas thin, (5) runny liquids, like water, have a low viscosity. 2.18. Gases Gases, like other (1) forms of matter, are made up of atoms that form groups called molecules. Gas molecules move very (2) freely, spinning around at high speeds and (3) filling up large spaces. As they move, the energetic gas molecules (4) collide with one another and with the walls of their containers. Vapour can also be classified as a gas, (5) although it behaves slightly differently. 2.19. What is Heat? Heat is a form of energy that (1) transfers from one object or body to another if there is a (2) difference in temperature between the two. When you are hot, for example, and the air (3) outside your body is cooler, you lose heat to the air. A change in a body's (4) level of heat results in a change in the energy of its molecules. This gives rise to a temperature change, which may in turn (5) lead to a change of state.