Temperature – the measure of the average kinetic energy of the particles in an object ◦ What is kinetic energy? ◦ So what does that tell you about the particles? All matter is made of tiny particles The particles are always in constant, random motion moving in all directions at different speeds The faster they move, the more kinetic energy they have Particles move faster in hot objects than in cooler objects. ( Figure 1 p. 158 and Q p.159) As temperature INCREASES, the average speed of the particles in random motion INCREASES Ex) The temperature in hot tea has a higher temperature of iced tea because the particles are moving faster on average SI unit for temperature = K (Kelvin) ◦ You can also use Celsius 8.2 Temperature There are two common temperature scales. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. The Celsius scale divides the interval between the freezing and boiling points of water into 100 degrees. 8.2 What temperature really is Atoms are in constant motion, even in a solid object. The back-and-forth jiggling of atoms is caused by thermal energy, which is a kind of kinetic energy. 8.2 What temperature really is Temperature measures the kinetic energy per molecule due to random motion. 8.2 Thermometers A thermometer is an instrument that measures the exact temperature. Most thermometers contain either a silvery fluid (mercury) or a red fluid, which is alcohol containing a small amount of red dye. 8.2 How a thermometer works The volume of alcohol in a thermometer contains huge numbers of alcohol molecules. As temperature increases, the alcohol molecules move faster and bounce off each other. The liquid alcohol expands and takes up more space in the thermometer. 8.2 Measuring temperature A thermistor is a device that changes its electrical resistance as the temperature changes. Some digital thermometers sense temperature by measuring the resistance of electrons passing through wire. 8.2 Liquid-crystal thermometers Some thermometers contain liquid crystals that change color based on temperature. As temperature increases, the molecules of the liquid crystal bump into each other more and more. This causes a change in the structure of the crystals, which in turn affects their color. 8.2 Absolute zero Absolute zero is -273°C. You cannot have a temperature lower than absolute zero. Think of absolute zero as the temperature at which atoms are “frozen.” 8.2 Converting to Kelvin The Kelvin temperature scale is useful in science because it starts at absolute zero. To convert from Celsius to Kelvin, you add 273 to the temperature in Celsius. Thermal Energy – the sum of the kinetic and potential energy of all the particles in an object (total energy of particles) ◦ Thermal energy increases as temperature increases ◦ Thermal Energy is also called ____________. When temp increases, KE increases Mass also affects thermal energy…if the temperature does not change, the thermal energy in an object increases if the mass of the object increases (more particles = more KE = higher temp) Unit: Joules Heat - Thermal energy that flows from something at a higher temperature to something at a lower temp Unit: Joules ( J) (it is a form of energy) Heat always flows from warmer to cooler material. Ex) Can you tell if someone has been sitting in your chair? How and why? Specific Heat – the amount of heat needed to raise the temperature of 1kg by 1 degree Celsius ◦ As a substance absorbs heat (like the ocean at the beach), its temperature change depends on the nature of the substance AND the amount of heat added Measured in J/(kg degree C) Water ◦ Compared to other materials, water has the highest specific heat ◦ Water can absorb heat without a large change in temp ◦ That makes it useful as a coolant ◦ EX) That is how it is used in automobile engines (if water temp is lower than the engine temp, heat will flow from the engine to the water) FIGURE 4 p.161 and Specific heat Discussion Q Measuring Specific Heat Calorimeter – measures using the mass, change in temp, and amount of heat absorbed or released A. Celsius B. Fahrenheit C. Kelvin D. Joules A. B. C. D. Cold to hot Warm to hot Hot to cold Heat does not travel A. Vibrate quickly B. Vibrate slowly C. Do not move D. They do not collide A. B. C. D. Expand Contract Slow down Glow Are overheated B. Reach supreme zero C. Reach absolute zero D. Are frozen A. Transfer of thermal energy by collisions and vibrations between particles in matter Occurs because particles are in constant motion ◦ Ex) If a spoon is heated by a flame on a Bunsen burner, what happens? Kinetic Energy of the Particles near the heat source (flame) increases These particles collide with neighboring particles, transferring kinetic energy The KE gets transferred from one end of the spoon to another Thermal energy gets transferred without changing or moving matter All materials can be conductors, but the heat moves differently in different objects Heat conducts faster in solids and liquids than in gases (Heat in gases moves more slowly because the particles are farther apart, therefore there are fewer collisions) Best Conductors are Metals (more freely moving electrons) Convection – transfer of thermal energy in fluids by the movement of warmer and cooler fluid from place to place (gases and liquids) Particles with a lot of energy collide with particles with less energy and transfer thermal energy The faster particles move, the more they spread apart ◦ Therefore, fluid expands as temperature increases Convection Currents – rising and sinking action that causes a transfer heat from warmer to cooler parts of the fluid – in both conduction and convection Deserts and Rain Forests ◦ ◦ ◦ ◦ atmosphere is made up of gases Atmosphere is warmer at equator than at poles Warmer on surface than at higher altitudes The temperature differences create convection currents P. 166 Visualizing Convection Currents How the sun’s heat travels through space Little matter exists in space between Sun and Earth, so heat must be transferred through radiation Radiation – transfer of energy by electromagnetic waves (which can travel through space even when no matter is present) This energy is often called Radiant Energy Ex) When you warm your hands by a fire Ex) Sun When radiation strikes a material, some of the energy is absorbed, some is reflected and some may be transmitted through the material The amount of energy is determined by the type of material. ◦ Light colored materials reflect more ◦ Dark colored absorb more radiant energy Convection B. Conduction C. Radiation A. A. B. C. D. Crust Mantle Outer core Inner core A. B. C. Heat falls and cold rises Heat rises and cold falls Heat and cold do not transfer A. B. C. D. The plastic popsicle stick The metal bowl The air around the flame They will conduct heat the same amount With a shoulder partner, come up with 2 examples of Conduction, Convection and Radiation Everyday examples: ◦ wearing a coat when it is cold outside ◦ using a cloth or pot handle to lift hot dishes out of the oven In these examples, you used materials to control the flow of heat Almost all living things have special features that help control the flow of heat ◦ Seal’s thick coat (keeps it from losing heat) ◦ Emperor penguins thick layer of blubber ◦ Thin, scaly skin of desert lizard (reflects sun’s rays) A material in which heat flows slowly (poor conductors) ◦ Wood, wool, fiberglass, some plastics, air ◦ Metals and other conductors of heat are poor insulators Gases, like air, are usually better insulators (air pockets heat poorly and keep convection currents from flowing) ◦ Fleece jackets work the same way – fleece fibers trap and hold air next to you, which prevents the flow of heat from your body Insulating buildings – protect from weather, keeps furnaces and ACs working efficiently, saving energy Why are good conductors of heat poor insulators? Predict whether plastic foam, which contains pockets of air, would be a good conductor or insulator. Explain. Critical Thinking Question Several days after a snowstorm, the roofs of some homes on a street have almost no snow on them, while the roofs of other homes are still snow-covered. Describe what would cause this difference. If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why? Why does hot air rise and cold air sink?