## 20141119

### Online reading assignment: temperature

Physics 205A, fall semester 2014
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on temperature.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Warming causes expansion. Cooling causes contraction. The longer the length, the less temperature change needed to expand it."

"The expansion of materials is what ultimately defines what a change in temperature 'is.'"

"Matter expands and contracts in response to changes in temperature. Different materials have different expansion coefficients."

"I found it very interesting how there are gaps in railroads, sidewalks, bridges, etc. I never thought about it but now I know that it is to prevent a warped shape from thermal expansion due to heat."

"I understand that we should buy gasoline when it is cold outside and the company does not adjust for temperature."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"Maybe explain '3·α.'"

"This section seems pretty straightforward. Similar to stretch and compression of object but based on temperature instead of applied force."

"I found the presentation about linear expansion confusing. I understand that change in temperature is important, but the formula was very confusing. Change in temperature being proportional to change in length over the original length doesn't click with me yet. I would definitely benefit from some talk about this in lecture."

For solids, what is the mathematical relationship between the coefficient of volume expansion β and the coefficient of linear expansion α?
"β = 3·α."

"Whoa--what?"

"The change in temperature."

"I am not sure and obviously could use some help with this in class."

To expand these two steel beams 1.0 cm from their original lengths, the longer beam will require __________ temperature increase compared to the shorter beam.
 a smaller. *************************** [27] the same. ******** [8] a larger. ************* [13] (Unsure/guessing/lost/help!) ****** [6]

For a thermometer, the glass volume expansion coefficient 3αglass is __________ the alcohol volume expansion coefficient βalcohol.
 less than. ****************************** [30] equal to. ********** [10] greater than. ******* [7] (Unsure/guessing/lost/help!) ******* [7]

For the water level in this plastic rainwater basin to lower as the temperature falls overnight, the plastic volume expansion coefficient 3αplastic must be __________ the water volume expansion coefficient βwater.
 less than. ********************** [22] equal to. ***** [5] greater than. ******************* [19] (Unsure/guessing/lost/help!) ******** [8]

A certain fuel company will measure out a gallon of gasoline and sell it for the same price, whether it is cool or warm. Indicate the gallon of gasoline that has a greater:
(Only correct responses shown.)
mass: the cool gallon [46%]
density: the cool gallon [74%]

Briefly explain why a gallon of gas purchased when it is cool would be better than a gallon of gas purchased when it is warm. (In either case, the fuel company dispenses the same volume of exactly one "standard" gallon.)
"When it is cold the gasoline would have a greater density and mass because the substance is more condensed than it would be when warm. When it is warm, the substance would expand, meaning you would get the same volume of gas with less density and mass."

"The mass of a cool gallon will be greater because the molecules are moving slower so they take up less area and will sit closer together."

"Well, when it is cold it will have more energy."

"...more holla for yo' dolla."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The difference between the densities of gasoline is so minuscule that it really doesn't matter to buy a given volume at a certain temperature." (Yes, but that small price difference multiplied by a lot of gasoline sold = PROFIT.)

"Isn't gas stored underground where it's kept at a constant temperature? And for that matter, isn't this entire dilemma an urban myth?" (Yes, and yes, if you assume that the gasoline does not get warmed up appreciably as it gets pumped through a warm above-ground dispenser. But see the above question and answer.)

"Gas in this area just went below \$3 a gallon. I think I was nine years old the last time it was that cheap."

"Are we allowed to skip the final if we are happy with our grade?" (Sure, that is entirely up to you. Your "take it or leave it" grade, which is the total of your course points without taking the final will be posted the weekend before finals week.)

"Are there any known materials that do not expand/contract due to temperature changes?" (Strictly speaking, no--but there are some exotic alloys that have very small expansion coefficients, used in super-large telescope mirrors or space-based telescope mirrors that experience large temperature swings, in order to minimize changes to their size/shape.)

"In addition to solids/liquids, will we also cover expansion/contraction of gases?" (No--that sounds dangerously like chemistry (P·V = n·R·T) talk to me...)