1. Matter and Energy

2. Drill February 8, 2016 Below are two equations we will soon become familiar with and use often. The left side of the classroom will calculate the UOM for h and the right side will calculate the UOM for k. First group to derive correct units wins. Hint : A Q with dot on top is equal to Q per unit time.

3. Matter and Energy Now let’s talk about the modes of heat transfer (the ways in which heat goes in/out of a system)… Heat (Q) – energy transfer caused by a temperature difference 1.Conduction 2.Convection 3.Radiation Q in is (+) Q out is (-)

4. Matter and Energy Heat (Q) – energy transfer caused by a temperature difference Thermodynamics - “the study of systems and energy transfer” ConductionConvectionRadiation

5. ??????????????????????? If 2050 Joules of heat is radiatively transferred into a surface over 25 seconds, what is the average rate of heat transfer?

6. Matter and Energy So far, we have defined heat transfer and talked about its sign convention… Heat (Q) – energy transfer caused by a temperature difference …but we haven’t talked about how heat is transferred. Q in is (+) Q out is (-)

7. Matter and Energy This man is holding one end of a metal rod inside of a furnace with his bare hands. Do you think that he can do that for very long? Heat (Q) – energy transfer caused by a temperature difference Why or why not? Conduction!!! Over time the rod heats up…

8. Matter and Energy Conduction Heat Transfer – energy transfer between molecules due to a temperature difference Heat (Q) – energy transfer caused by a temperature difference The parts of the rod inside the furnace heat up first. Over time, those molecules pass that heat along to the molecules near them that are outside the furnace. Eventually the whole rod heats up!

9. Matter and Energy The insides of a computer get very hot as it operates. How do we keep them from overheating? Heat (Q) – energy transfer caused by a temperature difference Computers use fans to cool down…just like us! This type of heat transfer is called Convection.

10. Matter and Energy Convection Heat Transfer – energy transfer due to the bulk motion of a fluid Heat (Q) – energy transfer caused by a temperature difference As the boards and chips inside the PC heat up, the fan turns on. The fan pulls in cool air from outside the PC which picks up the heat from the boards and chips. The now hot air is forced out of the PC, cooling it down.

11. Matter and Energy The temperature outside changes over time; it’s cool at night and warm throughout the day. Why? Heat (Q) – energy transfer caused by a temperature difference Radiant energy from the sun warms the earth during the day (when the sun is “up”). Radiant energy leaves the earth during the night, cooling the earth down (when the sun is “down”).

12. Matter and Energy The temperature outside changes over time; it’s cool at night and warm throughout the day. Why? Heat (Q) – energy transfer caused by a temperature difference

13. The finish line is in sight Define conduction, give an example Define convection, give an example Define radiation, give an example