## 20161116

Physics 205A, fall semester 2016
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.
"I understand how we've tied in stress to strain in solids to thermal stress changing an object's length. The material-dependent linear expansion coefficient characterizes the response of the material to thermal stress."

"When there is a change in temperature a material can expand lengthwise, so there needs to be a little 'give-and-take' room for materials to expand on contract."

"Different materials have different volume/length expansion coefficients, and that multiplied by change in temperature, you can thus get relative change in length or volume."

"When constructing buildings, it is important to take into account how much of a temperature change the area will go through because changes in temperature can cause strain."

"All elements have a coefficient that describes how their expansion/contraction rate is effected by changes in temperature. These coefficients can be used to compare the expansion of two compounds. Such as a thermometer and alcohol or a bucket and water."

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.
"I'm a little confused on why it says in solids, the material dependent thermal expansion coefficient for volume is three times the linear expansion coefficient. What is the linear expansion coefficient?"

"I don't really understand how the volume expansion coefficients come into play, I couldn't find the table for it in the book!"

"The difference about volume expansion β and linear expansion α."

"The examples for volume expansion were confusing. If you could go over them that would be great."

"I'm pretty good on this section I think. The example of the thermometer really helped. I was slightly confused about the 'overflow' part at first but I think I am okay on it now."

"I didn't find anything too confusing, but the expansion and contraction at different rates of a liquid inside a solid was a little confusing at first, but I'm pretty sure I understand it now."

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

"Linear expansion is the coefficient α (material-dependent), and volume expansion β is 3 times this because the volume is being solved for."

"They are both in units of (°C–1)."

"K–1."

"I have no idea :-("

"I honestly do not know."

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. *****************  [17] the same. *********  [9] a larger. ************  [12] (Unsure/guessing/lost/help!) ***  [3]

For a thermometer, the glass volume expansion coefficient 3αglass is __________ the alcohol volume expansion coefficient βalcohol.
 less than. ******************  [18] equal to. *******  [7] greater than. ****  [4] (Unsure/guessing/lost/help!) ************  [12]

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. ***************  [15] equal to. ** [2] greater than. ************** [14] (Unsure/guessing/lost/help!) ********** [10]

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 [34%]
density: the cool gallon [71%]

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.)
"When the gallon of gasoline is warm it expands and becomes less dense. Thus you are getting less for your buck."

"When the gasoline is purchased in cool weather, the density is greater."

"Because the density of that 'cold' gallon of gas would take up less volume than a normal gallon of gas, you would be getting more gas since they give you the same volume of gas either way."

"Because it will take up less room in the gas tank. Since the warm gasoline has expanded more then the colder gasoline, it will take up more room with less material, indicating you're at a full tank, when you could have more if it was colder."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"A little clarification on linear thermal expansion would be helpful."

"I am confused with the gasoline problem and why temperature causes a difference."

"Wouldn't it be easier to keep the gas warmer or cooler so you could sell a precise amount?"

"I'm having trouble understanding why gas stations can't regulate temperature more accurately. Does it really make that much of a difference?" (For filling up your car, not very much. But for selling vast amounts of warm gas to millions of customers, yes, there is a significant profit in the total difference.)

"The examples for volume expansion were confusing. If you could go over them that would be great."

"Just the normal examples usually done in class will help me."

"Interested in going through the problems on this page briefly in class if there's time."