Chapter 16 Thermal Energy and Heat

1. Chapter 16Thermal Energy and Heat Physical Science

4. Thermal Energy and Matter 16.1 • In 1700s, scientist thought heat was fluid called caloric • Not fluid or state of matter but related to motion • Work and Heat • Heat – transfer of thermal E from one object to another bc of temp difference • Flow from hot to cold • Can occur bc of friction from work • Temperature • Measure of how hot or cold bc of movement of particle • average kinetic E of the particles in an object due to random motion • all particle collisions transfer thermal E

6. Thermal Energy 16.1 • Total potential and kinetic E of all the particles • Depends on: • Mass • Cup of hot tea vs. teaspoon of hot tea • Same temp = so same average kinetic energy • Cup tea more thermal E b/c more particles • Temperature • Cup of hot tea vs. cup of cold tea • Same mass, same # of particles • Different average kinetic E = energy of particle higher in hot tea = greater thermal E • Phase (solid, liquid, gas) • Phase changes transfer thermal energy

7. Thermal Contraction and Expansion 16.1 • Thermal Expansion – increase in volume of material bc of temp increase  particles move faster  collide more often  expand • Gases expand more than liquids, liquids more than solids • bc force of attraction is less • Thermal Contraction • Temperature decreases  particles move more slowly  collide less often

8. Specific Heat 16.1 • Amount of heat needed to raise the temperature of 1 gram of a material by 1 degree • Lower specific heat = heat faster • Joules per gram per degree Celsius • Q = m(c)(ΔT)

9. Measuring Heat Change 16.1 • Calorimeter – instrument used to measure changes in thermal E • Used to measure specific heat of Al 

10. Math Practice # 1- 5 Page 477

13. Heat and Thermodynamics 16.2 • Conduction – transfer of thermal E • Not transfer of matter • Materials are TOUCHING • Slower in gases than liquids, liquids slower than solids • bc of particle location • Faster in metals bc electrons free to move (sea of e-) • Thermal Conductors – material that conducts well • Metal • Does not have to be hot  tile floor colder than wooden floor bc tile is a better conductor and transfers thermal E quickly to skin • Thermal Insulator – material that conducts poorly • Wood, air, plastic, foam

14. Convection 16.2 • Transfer of thermal energy when particles of a fluid (liquid or gas) move from place to place • Hot to cold • Convection current- fluid circulate in a loop as it alternately heats up and cools down • Occurs in oceans, weather, and movement of hot rock in Earth’s interior • Ovens

15. Radiation 16.2 • Transfer of E by waves moving thru space • All objects radiate energy • As temp increases, radiation increases

17. Thermodynamics 16.2 • The study of conversions between thermal energy and other forms of energy • 1st Law – energy is neither created or destroyed • 2nd Law – thermal E can flow from colder to hotter objects only when work is done • Relates to entropy (disorganization of system) • Heat engines –converts heat into work • Efficiency is always less than 100% • Waste heat = thermal E not converted to work • Spontaneous changes – makes system less orderly unless work is done • World is always becoming less orderly • 3rd Law – absolute zero (O K) cannot be reached

18. Solar Homes • http://www.youtube.com/my_playlists?pi=0&ps=20&sf=&sa=0&sq=&dm=0&p=CB817BBF0B24D9CA • 3 clips = 4 minutes

20. Heat Engines 16.3 • External Combustion Engine – an engine that burns fuel outside the engine • 1st used to pump water out of coal mines • Hot steam enters in right  valve slide to left  steam trapped  expands and pushes piston  heat converted to work

21. Figure 11 An External Combustion Engine

22. Figure 11 An External Combustion Engine

23. Figure 11 An External Combustion Engine

24. Heat Engines 16.3 • Internal Combustion Engines – Fuel burns inside the engine • Most use pistons that move in a cylinder • Each motion up and down = stroke • Linear motion is converted to rotary motion by crankshaft • Crankshaft = connected to transmission (linked to wheels and driveshaft • http://www.youtube.com/my_playlists • 6 min

25. Figure 12 An Internal Combustion Engine

26. Heating System 16.3 • Central heating system – heats many rooms from 1 central location • Commonly used electrical energy, natural gas, oil, and coal • Differ in how they transfer thermal energy • Hot-Water Heat • Circulating pump carries hot water to radiators in each room  conduction (water to radiator)  conduction and radiation (heating room) convection in room • Steam Heating • Similar to hot water heat but use steam instead • Often used in older buildings • Electric Baseboard Heating • Use electric energy (convert electrical to thermal) • Hot coils heat air by conduction and radiations  convection causes circulation • Space heaters are similar • Forced-Air Heating • Use fans to circulate air thru ducts to rooms  convection circulates air in room • b/c warm air rises, warm-air vents are located in floor • Advantage = air is cleaned as pass thru filters

28. Cooling Systems 16.3 • Heat pump – device that reverses the normal flow of thermal heat • Refrigerant – fluid that vaporizes and condenses inside the tubing of a heat pump • Absorbs heat  vaporizes  turns into gas • Gives off heat  condenses  turns into liquid • Heat pump must do work to refrigerant to reverse flow • Refrigerators- heap pump that transfers thermal E from cold food compartment to warm room • Open door adds more heat to room than it removes b/c coils get hotter • Air Conditioner • Must do work

30. http://www.expertvillage.com/video/165820_do-refrigerators-work.htmhttp://www.expertvillage.com/video/165820_do-refrigerators-work.htm • 2 minutes