Physics 1090: Fundamentals of the Physical Universe

Unit 4: Heat and Temperature
Due September 21, 2011
20 points

Answer one, and only one, of the following questions.

These questions are for you to combine different ideas from the unit and apply them to situations not directly addressed in class or in the textbook.  Think about the situation, and about the physics that applies to it.  See me for help if you are stuck.

1. Boiling away.

In the “Liquid Nitrogen Boil” activity, you (should have) found that freezing icewater with liquid nitrogen caused more of the nitrogen to boil away than freezing boiling water did.  Explain this result.  Include in your explanation:

• The role of heat (energy) in the boiling of any liquid,
• the specific conditions of the experiment, and
• the significance of the relative amounts of liquid nitrogen that were lost by boiling away.
 
2. Heat of melting.

Heating icewater causes the ice to melt, but the temperature of the icewater does not increase until after all of the ice is melted.  How can this happen?  Your explanation should cover:

• what heat is,
• what temperature is,
• why heating something ordinarily raises its temperature, and
• why the outcome is different for ice water.
 
3. Practical application.

Identify and describe a practical application of one of the principles explored in this unit.  Explain what the application is used for, and explain, using the principles of this unit, how it works.

4. Saunas and hot tubs.

It is not uncommon for the air in saunas and steam rooms to be maintained at 200 °F.  People can, and often choose to, spend twenty minutes or more in such environments without sufferng any ill effects.  However, spending even a few seconds in 200 °F water would be lethal.  How can the same temperature have such profoundly different effects on the human body?  Your explanation should cover:

• what temperature is,
• what causes an object’s temperature to change, and
• what factors determine how much its temperature changes.

Take your choice of these tasks.  Do not submit answers to more than one of them. Just choose one, and submit it.  Your answer should thoroughly address all points of the question.  An adequate answer will be several paragraphs long.

Warning: Do not turn in paper that has ragged edges!  If you write your work in a spiral-bound notebook, trim the edge before submitting it.  Papers with ragged edges will be returned unmarked.