The Physics
Hypertextbook
Opus in profectus

# Heat and Work

## Problems

### practice

1. Write something.
2. Write something else.
3. Write something different.
4. Write something completely different.

### conceptual

1. Three unrelated questions about ceiling fans.
1. A ceiling fan in a closed room (or even one with poor ventilation) does not make the room cooler. It actually increases the temperature of the air it pushes (not significantly, however). Why does this happen?
2. What does a ceiling fan do that would make people think (under certain circumstances) that it cools a room?
3. In really large heated spaces, ceiling fans are used to make the space occupied by people feel warmer. Why does this happen? (It has nothing to do with the phenomenon described in part a.)
2. A thought experiment. Two perfectly insulated, rigid chambers of identical shape and size are place side by side with a narrow opening connecting the two. The opening is initially blocked. One chamber is filled with a gas and the other contains a perfect vacuum. The opening is then unblocked. Determine the sign (+, −, 0) of the following quantities for the gas…
1. the heat added to (+) or removed from (−) the gas
2. the work done on (+) or by (−) the gas
3. the change in internal energy of the gas (+ temperature increased, − temperature decreased)
3. Two related questions.
1. Can a gas absorb heat without getting hotter? If so, how is it possible? If not, why is it impossible?
2. Can a gas absorb heat and not expand? If so, how is it possible? If not, why is it impossible?