Temperature

1. Temperature • 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

2. Particles move faster in hot objects than in cooler objects. ( Figure 1 p. 158 and Q p.159)

3. 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

4. 8.2 Temperature • There are two common temperature scales. • On the Fahrenheitscale, 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.

6. 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.

7. 8.2 What temperature really is • Temperature measures the kinetic energy per molecule due to random motion.

8. 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.

9. 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.

10. 8.2 Measuring temperature • A thermistoris 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.

11. 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.

12. 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.”

13. 8.2 Converting to Kelvin • The Kelvintemperature 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.

14. Thermal Energy • 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 ____________.

15. 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

16. Heat • 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?

17. Specific Heat • 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

18. Measuring Specific Heat Calorimeter – measures using the mass, change in temp, and amount of heat absorbed or released

19. Heat is measured in this SI unit: • Celsius • Fahrenheit • Kelvin • Joules

20. Heat moves from… • Cold to hot • Warm to hot • Hot to cold • Heat does not travel

21. Particles in a cold object: • Vibrate quickly • Vibrate slowly • Do not move • They do not collide

22. Substances ____ when they are heated • Expand • Contract • Slow down • Glow

23. Particles stop moving when they: • Are overheated • Reach supreme zero • Reach absolute zero • Are frozen

25. Conduction • 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

26. All materials can be conductors, but the heat moves differently in different objects • Heat conducts faster in solids and liquidsthan 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)

28. Convection • 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

29. 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

30. Convection Currents in the Earth

31. Explain what You think the colors in this simulated picture are showing.

32. Radiation • 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

33. 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

34. This type of heat transfer can travel through space • Convection • Conduction • Radiation

35. Convection currents take place in this layer of the Earth • Crust • Mantle • Outer core • Inner core

36. This is the relationship between hot and cold • Heat falls and cold rises • Heat rises and cold falls • Heat and cold do not transfer

37. If a plastic popsicle stick and a metal bowl are placed above a flame, which will conduct the heat best? • The plastic popsicle stick • The metal bowl • The air around the flame • They will conduct heat the same amount

43. Activity • With a shoulder partner, come up with 2 examples of Conduction, Convection and Radiation

44. Controlling Heat Flow • 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)

45. Insulators • 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

48. 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 QuestionSeveral 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.

49. 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?

50. Which type of heat transfer do the pictures below represent?