Heat and Thermal Energy

1. Heat and Thermal Energy “Molecules in the mosh pit” 9/14/2014 4

2. Today’s Warmup Today, something a little “different”. Here are some totally cool sidewalk chalk drawings (anamorphic illusions) by British artist Julian Beever.

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12. Today’s Warmup • Radiation, Conduction, Convection • Hip-hop Science…

13. Today’s Objectives • Intro to heat and thermal energy: • heat vs temperature • Measurement of heat • Definition of specific heat • Thermal energy BrainPop • CPS quiz next class period! • energy and heat

14. Thermal Energy Questions Vocabulary words Formulas Main Ideas Possible Test Questions Key Words Notes Notes Notes Notes Notes Notes Notes Notes Notes Notes Summary of the notes and information learned

15. What is “temperature” • Temperature is a measurement used to quantify the sensations of hot or cold, but what does temperature actually measure? • Molecules are constantly moving- they have kinetic energy. Some are moving quickly, some slowly, up, down, sideways… They bounce off each other like dancers in the mosh pit. • What happens when you heat molecules?

16. What is “temperature” • Heated molecules have more energy. They speed up and bounce around more. If we heat a cup of water all of the molecules increase their speed and random motion. • The temperature of an object measures the average kinetic energy of its molecules.

17. Thermal Energy (aka Heat) • The thermal energy of an object or substance is the TOTAL (SUM) energy (potential and kinetic) of its molecules • Mass, properties of the substance and temperature are involved here • For example- one cup of boiling water has less thermal energy (heat) than one gallon of boiling water- even though both are at the same temperature: 100 degrees C (212 degrees F).

18. Kinetic Theory • Kinetic Theory helps explain heat energy and heat transfer. • It says: all matter is made of constantly moving particles. • Let’s see that in action!

19. Kinetic Theory • Lab Activity • Work in groups of 4; One paper/graph per two students • Materials: • Stopwatch • 250 ml glass beaker • 100 ml ice • Thermometer • Hot plate • Take temperature measurements every 30 seconds until Mr. Rasure says to stop • Graph results

20. Kinetic Theory

21. Temperature Scales • The English system uses Fahrenheit to measure temperature. • In this scale water freezes at 32 degrees and water boils at 212 degrees. • Room temp is about 68 degrees.

22. Temperature Scales • Most of the world (and all scientists) use the Celsius scale- measured in degrees centigrade • Water freezes at 0 degrees Celsius and boils at 100 degrees. • Room temperature would be about 25 degrees.

23. Temperature Scales • To convert between the two use these formulas: • F = 1.8C + 32 • C = (F – 32) / 1.8

24. Temperature Scales • The Kelvin scale and absolute zero… • This temperature scale is named after the British mathematician and physicist William Thomson Kelvin, who proposed it in 1848. • Absolute zero is the lowest possible temperature where nothing could be colder, and no heat energy remains in a substance. Absolute zero is the point at which molecules do not move!

25. Conversion Practice • 1. Body Temperature = 98.6 °F (Convert to °C) • 1. °C = (°F - 32) X 5/9 °C = (98.6 - 32) X 5/9 = 66.6 X 5/9 = 37°C • 2. Boiling Temp of Water = 212 °F (Convert to °C) • 2. °C = (°F - 32) X 5/9 °C = (212 - 32) X 5/9 = 180 X 5/9 = 100 °C • 3. Moderate Oven = 175 °C (Convert to °F) • 3. °F = (°C X 9/5) + 32 °F = (175 X 9/5) + 32 = 315 + 32 = 347 °F • 4. Hot Summer Day = 38 °C (Convert to °F) • 4. °F = (°C X 9/5) + 32 °F = (38 X 9/5) + 32 = 68.4 + 32 = 100.4 °F

26. How does a thermometer work? • Thermometers work through thermal expansion. • As molecules are heated the gain kinetic energy and the volume of a substance increases • The liquid in a thermometer (colored alcohol or mercury) expands and rises in the glass tube as it gets warmer. • Digital thermometers work because of electrical resistance. The warmer a wire the more resistance it has to the flow of electrons.

27. Specific Heat • Different substances require different amounts of heat to rise to the same temperature- a wood handled pot of boiling water is much cooler to the touch than a steel handled pot of boiling water. • Why? • Conductors and Insulators…

28. Specific Heat • Specific heat is a property of a substance that tells how much the temperature goes up when a given amount of heat is applied. • Specific Heat = amount of energy needed to raise the temperature of 1 g of material 1 °C • A large/high specific heat means you have to put in a lot of energy for each degree increase in temperature.

29. Specific Heat • Water has a high specific heat • Water can “absorb” more heat/energy before its temperature rises…

30. Specific Heat Formulaas shown on TAKS chart . 8368 J/g °C Let’s Practice… for candy!

31. Specific Heat Ex: Calculate the amount of heat required to raise the temperature of 78.2g of water from 10C to 35C. Specific heat of water = 4.18 J/(gC) Heat = [4.18 J/(gC)] (78.2g)(35C - 10C) = 8171.9 J

32. Specific Heat Ex: Calculate the amount of heat required to raise the temperature of 78.2g of water from 10C to 35C. Specific heat of water = 4.18 J/(gC) Heat = [4.18 J/(gC)] (78.2g)(35C - 10C) = 8171.9 J

33. Thermodynamics- how heat moves • Thermal energy always travels from higher temperatures to lower temperatures • Thermal energy (heat) can be transferred in three ways: • Conduction • Convection • Radiation

34. Thermodynamics- how heat moves • Conduction- the transfer of heat by the direct contact of particles of matter

35. Thermodynamics- how heat moves • Heat continues to transfer until both objects reach thermal equilibrium (same temperature) • Materials that transfer heateasily are called conductors.Those that transfer thermalenergy poorly are calledinsulators.

36. Thermodynamics- how heat moves • Why would a Styrofoam cup not transfer the heat of hot coffee to your hand as quickly as a metal cup???

37. Thermodynamics- how heat moves • Convection- the transfer of heat by the actual motion of a fluid (liquid or gas) in the form of currents.

38. Thermodynamics- how heat moves • Radiation- the transfer of heat by electromagnetic waves. • Does not require matter to travel through (and thus can travel through the vacuum of space) • Transfers heat in all directions • Requires no contact • Can go through transparent materials

39. Thermodynamics- how heat moves • Electromagnetic waves can be: • Infrared • Visible light • Ultraviolet • The heat we enjoy from the sun comes to us as electromagnetic waves (radiation)

40. Thermal Energy Questions Vocabulary words Formulas Main Ideas Possible Test Questions Key Words Notes Notes Notes Notes Notes Notes Notes Notes Notes Notes Summary of the notes and information learned

41. Today’s Assignment • There are many types of heating and cooling systems found in the world around us including weather systems, living systems, and mechanical systems. Chapter 29 (pg. 471+) gives us an overview of these systems. • Lets use this chapter to answer the questions shown on page 489 (Concept Review #1 through 10). Write both the question and a complete answer. Use a clean sheet of paper you can turn in when complete.

42. CPS Quiz and Homework Sheet • You may use your notes/lab-book, BUT you may not share with your neighbor! • Subjects covered include: • Energy • Heat • Thermodynamics

43. Test Formulas F = 1.8C + 32 C = (F – 32) / 1.8 Ohm’s Law I = V/R (I=amps, V=volts, R=ohms of resistance)

44. Make it a great day Mustangs!