1. Midterm: 11-1150am, Friday Oct 10, 2008

2. Q0 (review question) A block slides on a surface with an initial velocity 5m/s. If the surface becomes rougher, 1)There will be more heat generated; 2)There will be less heat generated; 3)The same heat generated; 4) The heat generated depends on the distance it travels.

3. Summary : Energy transfer, work and energy conservation for open systems Work is an energy transfer due to mechanical forces. W= +Fd or -Fd

4. Three Steps C. If there are external forces, calculate the work done. W =+ Fd if an external force F is applied along the direction of motion; (s is the distance). W=-Fd if the force F is applied opposite to the direction of motion. Power= W/t, work done per unit time. A. Correctly identify “ system” and “external forces”. B. Identify kinetic energy, potential energy and thermal energy. E(final)=E(initial) if external forces are zero.

5. Phy100: Thermal energy Goals: Microscopic view of thermal energy; Dynamic equilibrium.

6. What is thermal energy? Thermal energy is a measure of how hot an object is. Temperature is a quantity that can be used to characterize the amount of thermal energy. More precisely, thermal energy is the total energy of microscopic motions of atoms (either vibrational or rotational but at atomic scales). HOT physically, motions of atoms speed up!!

7. Simulations on heat and thermal energy Microwaves heat up coffeeMicrowaves heat up coffee

8. Temperature units: ºC, K, ºF Kelvin Scale, Celsius/centigrade scale, Fahrenheit scale

9. Power as the rate of energy transfer Units: 1watt=1W=1J/s

10. Dynamic Equilibrium A) To maintain a const water level of a reservoir; B)To maintain a constant temperature of a house. The incoming mass or energy flux= the outgoing mass or energy flux; Or P(in) = P(out).