## 20191113

Physics 205A, fall semester 2019
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.
"Temperature plays a big role in thermal stress with expansion or contraction. This can be used to our advantage or disadvantage."

"I understand that if the liquid expansion is greater than the container expansion, there will be overflow. Vice versa, there will be no overflow. Expansion occurs as a response to temperature change."

"Explaining a thermometer: temperature ultimately 'is' something greater than the feeling that something is hot or cold; rather, change in temperature is the expansion of materials. In the case of a thermometer, the red alcohol experiences a temperature increase expanding its volume filling up more of the glass indicating a temperature change."

"It totally didn't occur to me how objects expand depending on differences in temperature. It just isn't something that's on my mind daily, but now that I've read about it, it clearly makes sense. I understood the concept of the length of steel beams and how shorter beams would require a higher temperature to expand compared to longer ones."

"The more heat applied the greater an object will expand the size of the expansion is proportional to the size of the object. The same is true for chilling an object."

"That the forces needed to prevent a solid object from expanding must be strong enough to counteract any change in length that would occur due to a change in temperature. It makes sense to me that the change in forces can result in serious structural damage."

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 do think I could use some extra examples covering linear thermal expansion and volume thermal expansion. These practice problems given were confusing to me."

"I had trouble understanding thermal stress and how it differs from normal stress. I was also confused by some of the equations for linear and volume thermal expansion."

"The linear and volume expansion formulas."

"I do not understand the concept behind why objects or fluids expand because of temperature change. Also, does heat mean expansion and cold mean shrink? Does it simply depend on the object?"

"I think I get the general concept of this, but I'm looking forward to the lecture and seeing how these equations will work out."

"Nothing was too crazy, just need to keep in mind how the equations work."

"The reading got more confusing as it went on. At the end, when it was discussing which time of day that the gas would be higher, I was not sure of the answer. "

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 mathematical relationship between the coefficient of volume expansion and the coefficient of linear expansion is that the coefficient for volume expansion is three times as much as the coefficient of linear expansion."

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. ******************* [19] the same. **** [4] a larger. **** [4] (Unsure/guessing/lost/help!) * [1]

For a thermometer, the glass volume expansion coefficient 3αglass is __________ the alcohol volume expansion coefficient βalcohol.
 less than. ************** [14] equal to. ****** [6] greater than. ****** [6] (Unsure/guessing/lost/help!) ** [2]

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. *********** [11] equal to. ***** [5] greater than. ************************ [24] (Unsure/guessing/lost/help!) ****** [6]

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 [35%]
density: the cool gallon [76%]

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.)
"Colder gasoline is more dense than warmer gasoline, so a cold gallon of gas contains more energy than a warm gallon of gas, even though they might cost the same."

"Chemically, cooling down allows for the molecules to slow and move closer together, allowing for the density to increase."

"When the gas is cooler it becomes denser and you actually end up with more molecules of gas per gallon."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This class is going by so fast!"

"Just need to talk this over in class."

"I never knew they had to account for expansion when constructing sidewalks."

"I would love to go over the gasoline question a bit more."

"Why do objects expand and shrink with temperature change?" (The atoms and molecules inside move faster when hotter. But because of asymmetry of the spring-like interactions between the atoms and molecules, it is harder for them to move closer together (because of mutual repulsion) than it is for them to move farther apart, and so overall the object will expand.)

"Will we be experimenting with liquids during the next lab?" (Actually, we'll be finishing up with standing waves for the last lab.)

"Sad you didn't dress up as an astronaut again for Halloween this year :("