Beginner's Guide to Rockets
Gas Temperature

Answers

1. Observations:
   Students should note that the balloon inflates after being placed on the heated flask.
   As the flask cools, the balloon is gradually pushed into the flask.
   
   
2. A. Compare the temperature of the gas molecules inside the flask with those outside the flask before heating.
   The temperature is the same inside as outside.
   
   B. Compare the temperature of the gas molecules inside the flask with those outside the flask during heating.
   The gas molecules inside the flask are at a higher temperature and therefore have a greater average kinetic energy than those outside the flask.
   
   C. Compare the temperature of the gas molecules inside the flask with those outside the flask after the balloon was placed securely on the flask.
   With the heat source removed, the gas molecules start to lose their kinetic energy to the surroundings. In so doing the gas molecules gradually slow down. Their average kinetic energy is reduced, and therefore their temperature drops.
   
   
3. A. How does the change in temperature affect the gas molecules' motion?
   The gas molecules' speed is reduced. Students should also note the consequent reduction in volume after cooling of the gas molecules inside the flask. Hopefully, students can make the connection between increasing temperature with an increase in volume.
   
   B. How does the change in temperature affect the gas molecules' force?
   As temperature decreases the gas molecules inside the flask exert a decreasing force on the balloon. The force per unit area (pressure) of the atmospheric gas molecules is relatively constant. Thus there is an unbalanced force acting on the balloon.
   
   
4. A. What happens to gas temperature as exhaust travels through a rocket nozzle from the combustion chamber to the exit?
   There is an overall decrease in temperature.
   
   B. How does molecular motion change from the throat to the exit?
   The nozzle converts the random motion of the molecules in the throat into a combination of random motion and ordered motion at the exit. The ordered motion is exhibited as exit velocity and produces thrust, the decreased random motion produces lower temperatures.
   
   C. What is one function of a rocket nozzle?
   To convert random motion into ordered motion and generate thrust.
   
   
5. What is the relationship between gas temperature and molecular motion?
   As molecular motion increases, average kinetic energy increases, and temperature increases.
   
   How did you form this conclusion?
   Answers will vary. The goal is for students to make the association between velocity of molecules with temperature. The is an important step. Encourage students to give a thoughtful, thorough explanation.
   
   
6. What is the relationship between gas temperature and force of gas molecules?
   Answers will vary. The goal is for students to make the association between increased temperature with increased force. Pressure is force per unit area.
   
   How did you form this conclusion?
   Answers will vary. This is an important part. Encourage students to give a thoughtful, thorough explanation.
   
   
7. After studying gas temperature and rocket nozzles, list three questions that you and your lab partners have about this topic.
   Answers will vary. The instructor may use this as a springboard to an extension to this lesson. The instructor may opt to explore questions as a class or to divide the class into small groups that will report their findings to the class. A good place to start is the Beginner's Guide to Rockets.