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 US
Freezing 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 Kelvin
used 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

7. Converting Temperatures
Fahrenheit 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 E
Across 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 is
Fahrenheit
Celsius
Kelvin
Thermocline

17. The temperature scale used in SI is
Fahrenheit
Celsius
Kelvin
Thermocline

18. The temperature scale used in science is
Fahrenheit
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 Expansion
Notice the cracks that have formed in the concrete after some time of thermal expansion

21. Transferring Thermal Energy
conduction – 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 Energy
insulators
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 Energy
convection – 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 Energy
Radiation – transfer by invisible radiation
electromagnetic waves
frequently called radiant energy

25. More on Radiation Emitters are substances that give off radiation
stars, 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 Transfer
Layers 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/s
Temperature conversions w/s