## 20151118

Physics 205A, fall semester 2015
Cuesta College, San Luis Obispo, CA

Students have a bi-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.
"Most substances contract when cooled and expand when warmed."

"Temperature is cool but we're really looking at how change in temperature effects the expansion of liquids and solids. Thermal stress causes strain in the solid or liquid causing a change in volume or length. The change in temperature is dependent on the coefficient of either volume or linear, it varies with material."

"Change such as expansion or contraction is due to the increase or decrease in temperature. Thats important for constructing things to account space for changes in material due to temperature."

"Heat causes expansion. The molecules get excited and take up more space."

"I understand why you would want to buy gasoline as it gets colder outside, because it gets more dense enabling more gasoline molecules in your tank."

"I understand that β is three times α because it accounts for volume which includes length, width and height. Change in temperature is basically causing the expansion of materials."

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.
"A lot of it."

"Still a little stuck on the gasoline question introduced. I'm guessing but that's not helping me at all."

"I am a bit confused on the thermometer concept. I understand that a liquid in a container will expand, and the container will also expand, but I don't know what that has to do with thermometers."

"Nothing really confused me this time. Then again, I didn't read the book this time, either. Coincidence?"

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

"The volume expansion coefficient is three times that of the linear expansion coefficient"

"They both have the same coefficient of inverse Kelvins."

"Whaaaa....?"

"Can you solidify these concepts?"

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. [18] the same. [9] a larger. [17] (Unsure/guessing/lost/help!) *** [3]

For a thermometer, the glass volume expansion coefficient 3αglass is __________ the alcohol volume expansion coefficient βalcohol.
 less than. [29] equal to. [4] greater than. [11] (Unsure/guessing/lost/help!) [3]

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. [20] equal to. [4] greater than. [18] (Unsure/guessing/lost/help!) [5]

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 [45%]
density: the cool gallon [74%]

Briefly explain why a gallon of gasoline purchased when it is cool would be better than a gallon of gasoline purchased when it is warm. (In either case, the fuel company dispenses the same volume of exactly one "standard" gallon.)
"The molecules in the cooler gallon are more tightly packed, so even though it's still a gallon there are more molecules leading to more available energy in the cooler gallon."

"The cold gallon will have a higher density and therefore would have more chemical bonds per unit volume thus more potential chemical energy."
"Because you get more bang for your buck."

"I don't know why the cool gasoline is better to purchase."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Thanks for the gas tip. =) I didn't think I'd ever actually use my physics knowledge for anything."

"When calculating the volumetric expansion of a vessel (barrel, glass tube, etc), does one consider the volume of both the container and of the space it contains? Do the vessel and the space within it always expand/contract in proportion to one another?" (Yes, and yes.)

"I could be right, or I could be horribly wrong. Can't wait to find out."

"Nothing really confused me this time. Then again, I didn't read the book this time, either. Coincidence?"

"Why do I have to pay for gas? Adulting is lame, I wanna spend my money on fun jazz not gas. Shall we start a riot?" (#ariotisthelanguageoftheunheard)

"Just found a Lightning McQueen spoon in my box of Frosted Mini-Wheats this morning. Today is a good day." (#‎todayisagooddaytodrive‬ #‎turnrighttogoleft‬)