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.
"That the length of an object changes by an amount by a change in the amount of ΔL when the temperature changes by a ΔT. With linear expansion, when there is a hole in a piece of solid material, when heated the hole will expand along with the material."
"A shorter beam will require a greater increase in temperature to expand to the same of a longer beam based on the equation. If a liquid is in a container it may expand to a greater, less than, or equal to the coefficient of its container."
"The material-dependent linear expansion coefficient characterizes the response of the material to thermal stress. The shorter beam will require a greater increase in temperature to expand the same amount as the longer beam. If the liquid and the container both expand the same amount for the same increase in temperature then the liquid will still fill the container to the brim."
"The linear expansion of an object tells as how the object responds to thermal stress. I also learned that mercury and alcohol thermometers work because the volume of the liquids expand or contract as the temperature changes."
"The relationship between temperature and the effects it has on the molecules of materials. If the temperature increases, the molecules' vibrations speed up and the object/material expands. If the temperature decreases, then the molecules' vibrations slow down and the object/material shrinks."
"Thermal stress causes strain. Linear expansion and volume expansions are unitless."
"Temperature change is really just the measurement of the volume expansion of the liquid inside of a thermometer compared to the expansion of the thermometer."
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 don't understand why the linear expansion coefficient is material dependent."
"Volume expansion--the water inside of a plastic bin. The water was at a lower level in the morning which means it contracted more than the plastic so I would assume it has a larger expansion coefficient?"
"The whole shorter beam needing more temperature change to increase the same length thing really messed me up for a second, because like shorter beam is less mass so like shouldn't it need less energy? But then somebody showed me the way that the equations work and it made sense."
"Volume expansion--I am not sure if it means that as the temperature rises, the volume increases of a substance. For instance, the alcohol in a thermostat rising as the temperature increases."
"How to understand when a coefficient for a solid is higher/lower than a liquid."
"How equations with ΔT can switch back and forth between Celsius and Kelvin units. That kind of tripped me up. I know that either can be used but I still found it a little confusing."
"I found the volume expansion kind of confusing when I first read about it. But after reading it over again I understand volume expansion and the equation for it."
"Everything makes sense."
"I did not get confused by any of this material."
For solids, what is the mathematical relationship between the coefficient of volume expansion β and the coefficient of linear expansion α?
"β = 3·α."
"Larger the linear expansion, the larger the volume expansion."
"Both coefficients are dependent on the type of material being measured. The coefficient of volumetric expansion is mathematically three times as much as the coefficient of linear expansion."
a smaller. ***************************** [29] the same. **** [4] a larger. ************ [12] (Unsure/guessing/lost/help!) *** [3]
less than. ******************************* [31] equal to. *** [3] greater than. ******* [7] (Unsure/guessing/lost/help!) ******* [7]
less than. ************* [13] equal to. **** [4] greater than. ************************ [24] (Unsure/guessing/lost/help!) ******* [7]
(Only correct responses shown.)
mass: the cool gallon [25%]
density: the cool gallon [70%]
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 another way to look at it is that a cold gallon of gas contains more energy than a warm gallon of gas."
"It's better to purchase a gallon of gasoline cool than when it is warm because gas is more dense when it is cool. Denser fluids have more mass so essentially when you fill your tank with cool gas you get more product for the same price per gallon."
"The hotter it is the more space between molecules. When cool the molecules move slowly when hot they move faster."
"I don't know--HELP!"
"If you buy gas when it is hot out you won't be able to put as much in your tank to make it full because it is hot and expanded. When it cools down, it will condense back its smaller form and you will have the same amount of gas but your tank won't be full?"
"I honestly don’t understand why it's better."
"Isn't mass and density the same?"
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Is the next midterm has only five questions?" (Yes, just like the previous midterm.)
"Please help with the gasoline question! thank you!"
"Please go over volume expansion coefficients."
"No questions today; this material seems to make sense."
"Would you rather live in an unexplored cave or in a treehouse in a remote forest?" (I choose treehouse.)
"How can fuel companies compensate for temperature-dependent volume changes of gas?" (They typically don't; so let the buyer beware.)
"I've been too focused on other classes and this totally slipped my mind."
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