1 Heat Unit 5- Lecture 3

2 Temperature is a measure of the average kinetic energy of the particles in the object. based on the motion of the particles in a substance fast motion = high temperature slower motion = lower temperature

3 Temperature relatively describes how the particles collide with the surface of the thermometer collisions transfer energy measured in K (kelvin) in SI system no degrees mark, same size divisions as Celcius

4 Temperature Scales Fahrenheit Common in the USFreezing point of water is 32ºF Boiling point of water is 212ºF Celsius Common in the rest of the world (SI) Freezing point of water is 0ºC Boiling point of water is 100ºC

5 Temperature Scales Kelvinused for science, as there are NO negative values 0 K is set at Absolute Zero, the temperature at which all particle motion stops Freezing point of water is 273K Boiling point of water is 373K NOTE – 100 K between freezing and boiling, so Kelvin uses the same degrees as Celsius

6

7 Converting TemperaturesFahrenheit to Celsius Cº = (5/9) * (Fº - 32º) Celsius to Fahrenheit Fº = (9/5) * ºC + 32 Celsius to Kelvin K = ºC + 273 Adjusts for differences in Zero temperature

8 Heat is a flow of energy from objects of higher thermal energy to objects of lower thermal energy heat is measured in Joules (J) because it is a form of energy described as a flow from hot to cold no such thing as “cold”

9 Specific Heat amount of energy needed to raise 1 kg of something by 1 ºC measured in: joules per kilogram degree Celcius J / (kg * ºC) is measured using a calorimeter represented by the variable “Cp”

10 Specific Heat note: water has an incredibly high specific heat value due to the bonds between water molecules this is why water is used as a coolant – because it will absorb a lot more energy before its temperature increases

11 Thermal Energy sum of the potential and kinetic energy of the object’s particles more particles  more mass  more thermal energy relationship: inverse / direct? faster moving  greater temperature  more kinetic energy  more thermal energy relationship: inverse / direct?

12 Thermal Energy changes in thermal energy :mass * change in temperature * specific heat kg * ºC * (J / [kg * ºC]) Q = m * C * (Tf - Ti) Q = m * C * ∆T

13 Because heat is a form of energy, heat is measured in …Watts Newtons Joules Mishbohah

14 Heat always flows… From low E to high E From high E to low EAcross layers of density Downwards, like gravity

15 The average motion of particles in a substance defines that substance’s…Heat Energy Potential Energy Temperature

16 The temperature scale used in the USA isFahrenheit Celsius Kelvin Thermocline

17 The temperature scale used in SI isFahrenheit Celsius Kelvin Thermocline

18 The temperature scale used in science isFahrenheit Celsius Kelvin Thermocline

19 Thermal Expansion as substances increase in temperature, the particles move apart substances expand and become less dense when heated substances shrink and become more dense when cooled explains expansion joints in bridges and concrete sidewalks water is one very important exception

20 Examples of Thermal ExpansionNotice the cracks that have formed in the concrete after some time of thermal expansion

21 Transferring Thermal Energyconduction – transfer by DIRECT particle contact heat [and electricity] moves faster in solids [to heat or cool] little to no resistance low specific heat best are metals because of “sea of electrons” that move between elements

22 Transferring Thermal Energyinsulators resist the flow of heat [& electricity] high specific heat resisted heat builds up and can cause substance to burn typically non-metals large molecules, no free electrons

23 Transferring Thermal Energyconvection – transfer by mass movement of particles transfer by fluid movement between warmer and cooler locations currents: warm expands [higher – less dense], cold contracts [lower – more dense]

24 Transferring Thermal EnergyRadiation – transfer by invisible radiation electromagnetic waves frequently called radiant energy

25 More on Radiation Emitters are substances that give off radiationstars, campfires, space heaters, etc. Absorbers capture radiation black shirts, asphalt, water Reflectors return most of the radiation that is emitted towards them mirrors, aluminum foil, ice & snow

26 Layers and Heat TransferLayers trap air in a “dead air space” More layers mean it’s harder to change temperatures between layers Ex. double-paned windows, dressing in layers, layers of construction on a house

27 What type of heat transfer describes cooking on an electric range?Conduction Convection Radiation

28 What type of heat transfer describes why a dark shirt feels warmer on sunny days?Conduction Convection Radiation

29 What type of heat transfer describes how a A/C system changes room temperature?Conduction Convection Radiation

30 What type of heat transfer describes how lake water is hot on top and cold on bottom?Conduction Convection Radiation

31 What type of heat transfer describes cooking in an electric oven?Conduction Convection Radiation

32 Homework If you’re not working well… you [individuals] will have an additional assignment If assigned and completed correctly, no penalty, no benefit If assigned and not completed correctly, will be – 15pts to your current accuracy score. Pg. 163 – Questions # 1- 4 Pg. 170 – Questions # 1 – 4

33 Homework If you’re working well….complete only Heat Calculations w/sTemperature conversions w/s