Warm-Up Exercise 8

Due 12:15 pm, Fri 14 Sep 2012

Physics 123, Fall 2012

Reading assignment: 20.4-20.6

What is a "state variable"? In your own words, and without referring to the text if possible, why do things like temperature, internal energy, volume, and pressure fall into this category?

Enter "-", "+", or "0" for the quantities Q, W, and ΔEint (three entries on each line) for the following situations (this is Quick Quiz 20.3 in the Eighth edition of the text).  (Note: newer editions of the textbook talk about W as the work done on the gas; older editions may describe W as the work done by the gas, which is the negative of the other W. I will try to always follow the newer convention.)
(A) Rapidly pumping up a bicycle tire (the system in question is the air in the pump)
(B) Lukewarm water in a pan on a hot stove (the system in question is the water in the pan)
(C) Air quickly leaking out of a balloon (the system in question is the air that was originally in the balloon)

Regarding the P-V diagram above, match the letters A-D to the appropriate path: isobaric, isovolumetric, isothermal, or adiabatic. Which processes do you think are more common in typical situations (motors, heaters, calorimeters, refrigerators, leaf blowers, etc.)?