## 20191125

### Online reading assignment: internal energy conservation

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 internal energy conservation.

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.
"Heat is a form of energy in the atoms and molecules of a substance or material, and that originates in the internal energy of a hot substance before flowing into a cold substance. I also understand that greater masses of materials require a greater amount of heat to fulfill their heat capacity in order to change its temperature."

"Internal thermal energy is the energy of an object on the inside of the object. Also temperature is a factor that plays into internal thermal energy; the higher the temperature, the more internal thermal energy there is."

"The effect that heat has on an object's thermal energy. As an object such as when meat has ice cubes put on it, it loses thermal energy; while when the meat is being cooked it gains thermal energy."

"That heat is a transfer of energy in joules, and because of this an object cannot 'have' heat. I also understand that heat flows from hot to cold; therefore, that heat comes from (or goes to) the internal energy of a substance."

"Internal energy conservation is a half-step away from our previous discussion of mechanical energy conservation in which we establish an equation and define which terms are increasing or decreasing. This transfer/balance equation is pivotal in discerning thermal internal energy changes."

"Objects with a higher internal thermal energy transfer that energy to objects with lower internal thermal energy. Heat refers to the transfer of thermal energy, while internal thermal energy refers to the temperature of an object."

"I understood what ∆Etherm is and why we calculate that instead of just Etherm."

"I understand that Q = m·c·∆T and that can be broken down as Qext = ∆Etherm, 1 + ∆Etherm, 1. This is a transfer/balance equation, thus one side of the individual ∆Etherm terms must increase and the other must decrease (if Qext = 0)."

"I don't understand anything."

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 found that the equation Q = m·c·∆T and the heat units other than the joule were confusing. I was not sure how to use them in a problem."

"I am a little confused on how to apply the specific heat equation to problems. How similar is this equation to calculating specific heat in chemistry? Are the units also the same as in chemistry, such as temperature always being measured in kelvins?"

"Identifying the different amounts of lost or gained internal thermal energy of objects. I understand that some objects lose energy and some gain energy but I do not understand how to find exactly how much is lost or gained."

"What I found confusing in the presentation preview was the transfer/balance equation. This confused me at first but then I realized that if the Q external energy transfer is equal to zero (if no heat is exchanged with the environment) then the changes in thermal energies of the objects add up to zero."

"Just need some practice on heat transfers. the transfer-balance equation should help."

"What is specific heat capacity?"

"In a calorimeter, it confuses me what loses energy and what gains energy. How can we tell what materials heat is flowing between and in what direction?"

"Something I didn't understand was some parts of the heat and internal energy. I don't understand the correlation of molecular kinetic energy with internal energy."

"There are a lot of concepts that are similar and I get them mixed up, heat, hot, temperature all sound the same to me, and the internal energy seems similar too."

"I remember this equation from chemistry and it ruined my grades. The individual problems were extremely confusing and I never knew which parts were given and which were not."

"I don't think I have any yet. I'll see when you explain it in class then I'll probably be confused."

"I understood all the topics in this reading assignment."

"I'm confused on everything."

"What I don't understand is if what is subtracted from what in ∆T. That is all I really need to go over."

"I don't understand what is occurring when cooking with the salt block. I was also lost when/what is doing work when there is a change in thermal energy."

"I didn't find anything confusing--just really want to try the salt block seafood now :)"

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:
 internal energy. *************** [15] temperature. ************** [14] (Both of the above choices.) ************ [12] (Neither of the above choices.) * [1] (Unsure/lost/guessing/help!) *** [3]

Raw seafood is placed on a block of salt that has already been heated up. The energy contained in the high-temperature block of salt is then transferred to the seafood, cooking it. While it is being cooked, the internal thermal energy of the seafood __________, while the thermal internal energy of the salt block __________.
 increases; decreases. **************************************** [40] decreases; increases. [0] does not change; does not change. * [1] (Unsure/lost/guessing/help!) **** [4]

For the seafood cooking on the salt block (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:
 seafood. ************ [12] salt block. ** [2] (There is a tie.) ************************* [25] (Unsure/lost/guessing/help!) ****** [6]

Frozen meat is placed in a water bath, in order to defrost it. At the very start of this defrosting process (where the frozen meat just begins to warm up from its below-freezing temperature, and the ice crystals inside have not yet reached the melting point), the internal thermal energy of the meat __________, while the thermal internal energy of the water __________.
 increases; decreases. ********************************** [34] decreases; increases. ****** [6] does not change; does not change. [0] (Unsure/lost/guessing/help!) ***** [5]

For the frozen meat in the water bath (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:
 frozen meat. ****** [6] water bath. ******* [7] (There is a tie.) ************************** [26] (Unsure/lost/guessing/help!) ****** [6]

A shot of whiskey is mixed with a pint of beer to make a boilermaker. Assuming that the whiskey and beer have approximately the same temperature before they are mixed together, the internal thermal energy of the whiskey __________, while the thermal internal energy of the beer __________.
 increases; decreases. ** [2] decreases; increases. ****** [6] does not change; does not change. ********************************* [33] (Unsure/lost/guessing/help!) **** [4]

For the shot of whiskey being mixed with the pint of beer (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:
 shot of whiskey. *** [3] pint of beer. ***** [5] (There is a tie.) ********************************* [33] (Unsure/lost/guessing/help!) **** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are there real life situations in which external conditions do not affect the thermal temperatures of the subjects?" (Stuff in a well-insulated cooler.)

"Seems straightforward."

"The transfers confuse me a lot unfortunately."

"Some of this heat stuff seems like it can be counterintuitive."

"How do we handle cases when there is heat exchanged between the system and the environment?" (In the transfer-balance equation, then you have a non-zero term for heat on the left-hand side of the equation, similar to non-conservative work being non-zero on the left-hand size of the equation for mechanical energy conservation.)

"If two objects come into contact with each other and have the same internal temperature, is there no change in internal energy?" (Correct.)

"Whiskey should never ruin a good beer."

"BBQ or sous-vide steak?"

"I'm just hungry really."

"I really want an 'A' in this class but that's not happening :/"

"I'm sorry I am super-sick."