FIG. 4-1 The heat content of a given substance depends upon both its mass and its temperature. A pail of cool water contains more heat than a cup of boiling water.

FIG. 4-2 A liquid-in-glass thermometer. Mercury or a colored alcohol solution responds to temperature changes to a greater extent than glass does, and so the length of the liquid column is a measure of the temperature of the thermometer bulb.

FIG. 4-3 A bimetallic strip thermometer. No matter on which side the heat is applied, the bend is away from the more expansive metal. The higher the temperature, the greater the deflection. At low temperatures the deflection is in the opposite direction. Steel and copper are often used in bimetallic strips; the steel expands less when heated.

FIG. 4-4 The color of an object hot enough to glow varies with its temperature roughly as shown here.

FIG. 4-5 Comparison of the celsius and fahrenheit temperature scales.

FIG. 4-6 To raise the temperature of 1 kg of water by 1° C, 4.2kJ of heat must be added to it. The same amount of heat must be removed to cool the water by 1° C.

FIG. 4-7 If 4.2 kJ of heat is added to or removed from 1 kg of other substances, their temperatures change by more than the 1°C change produced in water.

FIG. 4-8 The three mechanisms of heat transfer.

FIG. 4-9 Solids, liquids, and gases. A solid maintains its shape and volume no matter where it is placed; a liquid assumes the shape of its container while maintaining its volume; a gas expands indefinitely unless stopped by the walls of a container.

FIG. 4-10 The volume of water in this bathtub is equal to the product (length) (width) (height).

FIG. 4-11 Pressure is force per unit area. A force of 150 N applied to a piston of area 0.001 m² in a tire pump results in a pressure of 1.5 x 10⁵ N/m² = 1.5 x 10⁵ Pa.

FIG. 4-12 The human circulatory system. The heart consists of two pumps, called ventricles. The contraction and relaxation of the muscular walls of the ventricles take the place of the piston strokes of an ordinary pump. The right ventricle pumps blood from the veins through the lungs, where it absorbs oxygen from the air that has been breathed in and gives up carbon dioxide. The oxygenated blood then goes to the more powerful left ventricle, which pumps it via the aorta and the arteries to the rest of the body. A typical rate of flow of blood in a resting person is 6 L/min.

FIG. 4-13 An aneroid barometer. The flexible ends of a sealed metal chamber are pushed in by a high atmospheric pressure. Under low atmospheric pressure, the air inside the chamber pushes the ends out.

FIG. 4-14 Archimedes' principle. The buoyant force F_b on an object immersed in water (or other fluid) is equal to the weight of the body of water displaced by the object.

FIG. 4-15 Boyle's law: At constant temperature, the volume of a sample of any gas is inversely proportional to the pressure applied to it. Here p₁V₁ = p₂V₂ = p₃V₃.

FIG. 4-16 Charles's law: At constant pressure, the volume of a gas sample is directly proportional to its absolute temperature T_K, where T_K = T_C + 273°. Here V₁/T₁ = V₂/T₂ = V₃/T₃.

FIG. 4-17 The absolute temperature scale.

FIG. 4-18 Graphic representation of Charles's law, showing the proportionality between volume and absolute temperature for a gas at constant pressure. If the temperature of the gas could be reduced to absolute zero, its volume would fall to zero. Actual gases liquefy at temperatures above absolute zero.

FIG. 4-19 The molecules of a gas are in constant random motion.

FIG. 4-20 Gas pressure is the result of molecular bombardment. For simplicity, only vertical molecular motions are shown.

FIG. 4-21 Origin of Boyle's law. Expanding a gas sample means that its molecules must travel farther between successive impacts on the container wall and that their blows are spread over a larger area, so the gas pressure drops.

FIG. 4-22 According to the kinetic theory of gases, at absolute zero the molecules of a gas would not move. More advanced theories show that even at 0 K a very slight movement will persist.

FIG. 4-23 Compressing a gas causes its temperature to rise because molecules rebound from the piston with more energy. Expanding a gas causes its temperature to drop because molecules rebound from the piston with less energy.

FIG. 4-24 Molecular models of a solid, a liquid, and a gas. The molecules of a solid are firmly attached to one another; those of a liquid can move about but stay close together; those of a gas have no restrictions on their motion.

FIG. 4-25 The particles of a solid can be imagined as being held together by tiny springs that permit them to vibrate back and forth. The higher the temperature, the more energetic the vibrations. When a solid is squeezed, the springs are (so to speak) pushed together; when it is stretched, the springs are pulled apart.

FIG. 4-26 Evaporation. Alcohol evaporates more rapidly than water because the attractive forces between its molecules are smaller. In each case, the faster molecules escape. Hence the average kinetic energy of the remaining molecules is lower and the liquid temperature drops.

FIG. 4-27 The heat of vaporization of water is 2260 kJ/kg.

FIG. 4-28 The heat of vaporization of water is 2260 kJ/kg.

FIG. 4-29 The orderly arrangement of particles in a crystalline solid changes to the random arrangement of particles in a liquid when enough energy is supplied to the solid to overcome the bonding forces within it.

FIG. 4-30 A graph of the temperature of 1 kg of water, originally ice at -50°C, as heat is added to it.

FIG. 4-31 The various changes of state.

FIG. 4-32 An idealized heat engine. A gas at 200° C gives out more energy in expanding than is required to compress the gas at 20°C. This excess energy is available for doing work.

FIG. 4-33 A heat engine converts part of the heat flowing from a hot reservoir to a cold one into work. A refrigerator extracts heat from a cold reservoir and delivers it to a hot one by doing work that is converted into heat..

FIG. 4-34 A four-stroke gasoline engine.

FIG. 4-35 A typical refrigeration system. Heat is absorbed by the refrigerant from the storage chamber in the evaporator and is given up by the refrigerant in the condenser.

FIG. 4-36 In a steam turbine, steam moves past several sets of rotating blades on the same shaft to obtain as much power as possible. The stationary blades direct the flow of steam in the most effective way.

FIG. 4-37 Energy flow in electric generating plants. A large part of the energy waste is due to the unavoidable thermodynamic inefficiency of the turbine.

FIG. 4-38 The second law of thermodynamics provides a way to distinguish between processes that conserve energy and (a) increase entropy, hence are possible, and those that (b) decrease entropy, hence are impossible.