HEAT

1. HEAT By Mr. Martin

2. Temperature • Temperature – “is a measure of the average kinetic energy of the particles in an object.” Holt, Earth Science California (“ES”) (2001) page 214. • The more kinetic energy, the higher the temperature • Temperature is an average measure. A cup of coffee poured from a large pot of coffee both have the same temperature. (Later we learn than the pot of coffee has more heat, however.)

3. Measure Temperature with a Thermometer • Thermometers typically have a liquid like mercury or alcohol in a glass tube • As the kinetic energy of a substance increases, the substance expands (thermal expansion) • When you put a thermometer into a hot substance the liquid expands • When you put the thermometer into a cold substance, it contracts

4. Temperature Scales - Celsius • Making a Celsius thermometer • Take a glass tube partially filled with alcohol colored red • Put it in ice cold water. Mark this zero. • Put it in boiling water. Mark this 100. • Between these two marks put 98 equally spaced marks. You can also put marks the same distance apart below zero and above 100. • You can now use your thermometer to measure the temperature of anything

5. Questions: • Why red alcohol? • Why base the scale on the freezing and boiling of water? • Fahrenheit used the temperature of ice water with a salt as zero. 32º was the temperature of ice water. Water boils at 212ºF. Anything wrong with the Fahrenheit scale? • Only three countries officially use the Fahrenheit scale today – the U.S., the Cayman Islands and Belize. What’s up with that?

6. Kelvin • The Kelvin scale is the official SI unit although Celsius is routinely used in most countries and in science • An interval in the Kelvin scale is the same as a degree in the Celsius scale • 0 K is equal to -273º Celsius. 0 K is called absolute zero. That’s the theoretical temperature where all kinetic energy is lost.

7. Temperature Conversions • Water Freezes at 0ºC and 32ºF. • Water boils at 100º and 212Fº. • There are 100 degrees Celsius between the freezing and boiling points of water. • There are 180 degrees Fahrenheit between the freezing and boiling points of water. (212 – 32 = 180)

8. Slope Intercept y = mx + b b = 32 212ºF 32ºF 0ºC 100ºC

9. Solve for C

10. Conversions With Kelvin Scale

11. Heat and Thermal Energy • Heat – “is the transfer of energy between objects that are at different temperatures.” ES at 219. • Thermal energy is what is being transferred. Thermal energy “is the total kinetic energy of the particles that make up a substance.” Id. at 220. • While a cup of coffee being poured from a large pot of coffee may have the same temperature, the pot of coffee has more thermal energy since it has more of the coffee.

12. Thermal Energy - Joules • Thermal energy is measured in joules (J). You can figure this out. Work or energy = F x d. You know from last year that F=ma. A=d/t/t. If you put all units together for each of these formulas you get the units above.

13. Thermal Equilibrium • Thermal Equilibrium – “the point at which two objects reach the same temperature; at thermal equilibrium, no net transfer of thermal energy occurs.” (ES, Glossary, page 598. See also page 220.)

14. Energy Transfer - Conduction • Conduction – “the transfer of thermal energy from one substance to another.” (ES p. 221) Demo. If time, QuickLab p. 221. • Conductors transmit thermal energy well • Insulators don’t transmit thermal energy well. • Thermal conductivity – “the rate at which a substance conducts thermal energy.” ES 224.

15. Energy Transfer - Convection • Convection – “the transfer of thermal energy by the movement of a liquid or gas.” (ES at 222.) • Demo

16. Energy Transfer - Radiation • Radiation – “the transfer of energy through matter or space as electromagnetic waves, such as visible light or infrared waves.” • E.g. light from the sun. • Greenhouse effect - earth reflects back infrared waves. The earth’s atmosphere prevents some of the infrared waves from being reflected back into space.

17. Heat Capacity • Heat capacity is the amount of heat required to change a substance’s temperature by a given amount. (http://en.wikipedia.org/wiki/Heat_capacity ) • Specific heatcapacity is the amount of energy needed to change the temperature of 1kg of a substance by 1ºC. (ES at 224) • Measured in (J/kg)(ºC)

18. Water – High Heat Capacity • Water has a very high specific heat capacity. It takes a lot of heat energy to raise the temperature of water. • Important in coastal areas like San Diego. • We have relatively cooler temperatures in the summer compared to inland areas since the ocean waters do not heat up as easily as land. • We have relatively warmer temperatures in winter since the ocean retains a lot of thermal energy. • Water heats up slowly. Water cools down slowly.

19. Calculating Heat • Heat (J) = specific heat capacity in (J/kg)(ºC) x mass (kg) x temp. change (ºC). • The kg and ºC cancel leaving you with Joules • Energy to raise cup of tea from 25 ºC to 80 ºC. • Specific heat water = 4,184J/kg(C) • Cup of water about .2kg • Change in temperature 80-25= 55 ºC • You Try – Math Break page 225

20. Calories • A calorie (cal) is the amount of energy needed to raise the temperature of 1 gram of water 1 ºC • One calorie = 4.184 J • 1 Kilocalorie = 1,000 calories = 4,184 Joules • Also written as Calorie with a capital C. When we talk about Calories of food, we are referring to Kilocalories

21. States of Matter • Solid –particles held tightly in place • Liquid – particles not held as tightly in place. Can slide past one another. • Gas – particles move freely. • See generally http://www.chem4kids.com/files/matter_states.html

22. Changes of State • A change in the physical form of matter • Melting - Solid to liquid – e.g. ice to water • Boiling - Liquid to gas – e.g. water to steam • Freezing – Liquid to solid – e.g. water to ice • Condensing – Gas to liquid – e.g. water vapor to water as when a Diet Coke filled with ice “sweats” • Sublimation – solid to gas – e.g. ice to water vapor

23. Heat During Changes of State steam Water+ steam 100ºC water Ice + water 0ºC Ice Energy

24. Heat Technology • Radiator hot water heating • Warm air heating – this is what we typically have in our homes. Forced air heating. Typically uses natural gas to heat. • Insulation • Home • You • Solar heating • Passive • Active • Water • Contrast solar voltaic

25. Heat Engines • Internal Combustion Engines – • 4-stroke internal combustion engine demonstration, http://www.youtube.com/watch?v=uB2cmkWbCMI • 4 Cycle Internal Combustion Engine - Mechanical Parts, http://www.youtube.com/watch?v=wRIKJ6Av5zo

26. Cooling • Ceiling and Room Fans • Do not actually cool the room. The movement of air, however, removes hot air near your skin. You feel cooler. Shut them off when not in room. • If you are sweating they also increase evaporation removing heat from your body. • A fan uses a small fraction of the electricity that an air conditioner uses. Air conditioners are the highest electricity uses in most households. • Whole House Fans • When the temperature has cooled outside, whole house fans circulate cool air from the outside through the house and out through the attic. As a result the house and attic become significantly cooler. They are especially useful in places like San Diego where we often have rapid decreases in temperature at night.

27. Cooling continued • Evaporative coolers – Take a fan. Put a moist towel in front of it. The water in the towel evaporates – i.e. changes from liquid water to a gas. This change of state takes energy. (Remember are graph earlier.) Where does the energy come from? The air. Heat energy is removed from the air making the air actually cooler. Evaporative coolers were popular before air conditioners. They are most effective in hot, dry climates. They are not very effective if it is humid. They use much less energy than air conditioners.

28. Cooling – Air Conditioners • Heat is absorbed when a liquid evaporates • Instead of water, air conditioners use a refrigerant that evaporates at a low temperature • Hot air flows over cold evaporator coils causing the refrigerant to evaporate and absorb heat

29. Air Conditioners - continued • To continue the process you have to change the gas back to a liquid • To do this a compressor compresses the gas changing it back into a liquid • This creates heat which passes over condenser coils and is vented to the outside with fans • See http://home.howstuffworks.com/ac.htm

30. Heat Technology and Thermal Pollution

31. Heat Island Effect • http://www.epa.gov/hiri/