1. 10.2 Defining Heat pp. 365 - 370 Mr. Richter

2. Agenda  Finish Temperature Notes  Introduction to Heat  Notes:  Heat and Energy  Heat and Temperature  Heat and Work  Conservation of Energy  Tomorrow: Finish Notes from 10.2  Friday: Work on Science Fair Posters  Monday: Phase Change Lab

3. Objectives: We Will Be Able To…  Explain heat as the energy transferred between substances that are at different temperatures.  Relate heat and temperature change on the macroscopic level to particle motion at the microscopic level.  Apply the principle of energy conservation to calculate changes in potential, kinetic and internal energy.

4. Defining Heat Again: non “How hot or cold something is”

5. What is Heat?  When two substances have different temperatures their molecules have different amounts of kinetic energy.  When those molecules touch, they transfer some of the energy from one to the other (think collisions).  Heat is the energy transferred between objects because of a difference in their temperatures.

6. What is Heat? A closer look. The can is warm and the water is cold. The can and the water have equal temperatures

7. Heat and Energy  Because heat is the transfer of energy, heat has the units of energy: joules (J).  Other units (not used in physics):  Calories  BTUs (British thermal units)  therms  Energy transfer only happens when there is a difference in temperatures, so heat is only perceived when objects have a different temperature.

8. Heat and Work Conservation of Energy

9. Heat and Work  As previously discussed, mechanical energy (potential and kinetic) is always conserved in the absence of…  …friction.  Any mechanical energy that is not conserved becomes internal energy (U).  Internal energy comes primarily from:  friction  deformation (think car crashes)

10. Heat and Work: Examples  When a nail is hammered into wood, and then removed the nail feels hotter.  Kinetic energy became internal energy.  Don’t believe me?  Rub your hands together vigorously.

11. Heat and Conservation of Energy  Total energy (of any kind) is conserved if we include internal energy.

12. Practice Problem  A 3.0 g copper penny drops a distance of 50.0 m to the ground. If 65% of the initial potential energy goes into increasing the internal energy of the penny, determine the magnitude of that increase.  U = 0.96 J

13. Wrap-Up: Did we meet our objectives?  Explain heat as the energy transferred between substances that are at different temperatures.  Relate heat and temperature change on the macroscopic level to particle motion at the microscopic level.  Apply the principle of energy conservation to calculate changes in potential, kinetic and internal energy.

14. Homework  p. 370 #1-4 due Friday