Online reading assignment: internal energy conservation

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 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.

"It is not correct to say that a substance contains heat. The substance contains internal energy. Heat is the energy transfer from hot to cold."

"I somewhat understand thermal internal energy and how it is evaluated by the movement of microscopic atoms."

"I understood the equation Q = m·c·∆T as something I have done in chemistry. It is interesting now in physics."

"A low temperature object has little thermal internal energy and a high temperature object has more thermal internal energy. If temperature increases, heat from the environment is being transferred to the object and thermal internal energy increases. The opposite occurs when an object is cooled and transfers heat from the object to the environment. A system with Q = 0 is insulated from the envirnonment and there is no transfor of heat."

"I understand how to plug in things into the equation Q = m·c·∆T."

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.

"What is our definition of the system that we are working with? I know there are many types of them, could we go over the language of how to describe what is happening in a system?"

"I don't understand how to figure out which object loses more internal energy."

"Still a little bit fuzzy how this relates to mechanical energy and work."

"I'm feeling good on this material so far."

"Not much was confusing, would maybe help just going over an example of calorimetry."

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:

internal energy.	****** [6]
temperature.	********** [10]
(Both of the above choices.)	********** [15]
(Neither of the above choices.)	* [1]
(Unsure/lost/guessing/help!)	** [2]

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.	******************************** [32]
decreases; increases.	* [1]
does not change; does not change.	[0]
(Unsure/lost/guessing/help!)	* [1]

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.	********** [10]
salt block.	***** [5]
(There is a tie.)	****************** [18]
(Unsure/lost/guessing/help!)	* [1]

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.	********************** [22]
decreases; increases.	******* [7]
does not change; does not change.	**** [4]
(Unsure/lost/guessing/help!)	* [1]

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.	**** [4]
water bath.	******* [7]
(There is a tie.)	******************** [20]
(Unsure/lost/guessing/help!)	*** [3]

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.	* [1]
decreases; increases.	* [1]
does not change; does not change.	****************************** [30]
(Unsure/lost/guessing/help!)	** [2]

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.	[0]
pint of beer.	** [2]
(There is a tie.)	***************************** [29]
(Unsure/lost/guessing/help!)	*** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I am confused with heat transfers between internal energy systems and when there may be a tie or not." (If there are only two internal energy systems that interact, then the amount they change will be a tie (one will be an increase, the other a decrease) as long as there are no third parties: one or more other internal energy systems, and/or heat losses/gains from the environment.)

"Why are we measuring temperature in kelvin?" (When we're doing chemistry, we do as chemists physicists do.)

"I observed three candles burning side by side. The candle in the center melted much faster than the two outer candles. What is the energy transfer relationship taking place?" (Radiative heat transfer!)

"Wouldn't the salt block have experienced the greatest changes in energy because it is heated up then losing heat from it transferring to the seafood?" (Perhaps, but the process of interest is after it is heated up, and the seafood is placed on it. Also, if the process is heating up the salt block, then it loses heat, the net change in internal energy wouldn't be very much.)

"Can we use the same technique for finding non-conservative energy loss for internal thermal energies as we did with mechanical energy forms?" (Yes. The transfer-balance equation, but with heat instead of work, and internal energy changes instead of mechanical energy changes.)

I'm slightly confused at the concept of heat flow. Why does the hotter object give off thermal heat to the colder object? It makes sense but I would like to know the chemical reason for this transfer of energy." (It has something to do with entropy, but even in collisions in cars we've seen how a faster car can transfer some of that translational kinetic energy to a slower car. Similarly for ideal gases, a faster (higher temperature atom) will transfer some of its internal energy to a slower (lower temperature) atom.)

"Will there be any more extra credit opportunities before the final?" (I'll look into it. But be sure to maximize the regular points remaining in this semester.)