drsckng3 Posted December 21, 2007 Share Posted December 21, 2007 If I stirred the water in the beaker vigorously for 3 minutes, will the temperature of the water increases, decreases or stay constant? Link to comment Share on other sites More sharing options...
iNow Posted December 21, 2007 Share Posted December 21, 2007 What happens to all of the molecules of water as you stir them? Link to comment Share on other sites More sharing options...
ydoaPs Posted December 21, 2007 Share Posted December 21, 2007 What is temperature? Link to comment Share on other sites More sharing options...
MrMongoose Posted December 21, 2007 Share Posted December 21, 2007 It depends on the initial water temperature, ambient temperature, speed of stirring, size of stirring device and the shape of the water. If you sit outside in the winter with a mug of tea, its going to take a lot of stirring to stop it from going cold. Link to comment Share on other sites More sharing options...
iNow Posted December 21, 2007 Share Posted December 21, 2007 It depends on the initial water temperature, ambient temperature, speed of stirring, size of stirring device and the shape of the water. No, actually, it doesn't. The question gave three possible answers: it heats, it cools, it stays the same. The only act described was the stirring. None of the variables you suggest are relevant to this particular question. If you sit outside in the winter with a mug of tea, its going to take a lot of stirring to stop it from going cold. This is an interesting tip to the OP (while not relevent to the actual question, it may help them understand the concept). We should all probably wait until they respond letting us know what THEY think before we give too much more information. Link to comment Share on other sites More sharing options...
MrMongoose Posted December 21, 2007 Share Posted December 21, 2007 No, actually, it doesn't. The question gave three possible answers: it heats, it cools, it stays the same. The only act described was the stirring. None of the variables you suggest are relevant to this particular question. I'm interested to hear what you have to say but I disagree. The rate of work input is a function of the stirring speed and the size and shape of the spoon. And as there's nowhere for the work to go other than to be converted to heat by friction, this is the rate of heat input by stirring. Heat transfer between the beaker and its surroundings is a function of the temperature difference for conduction and convection and of difference between temperatures raised to power 4 for radiation, so the rate of heat flow into/ out of the beaker depends on temperature difference. The change in sensible heat is equal to the rate of work in minus the rate of heat flow out, so if work in is equal to heat out, the sensible heat will remain constant; if the work in is greater than heat out, sensible heat will decrease; and if the heat out is greater than the work in, sensible heat will decrease. Temperature is proportional to sensible heat. This is an interesting tip to the OP (while not relevent to the actual question, it may help them understand the concept). We should all probably wait until they respond letting us know what THEY think before we give too much more information. I'm probably coming across as awkward, but I'm just trying to provoke deeper thought so that this simple homework question can lead to greater things! Link to comment Share on other sites More sharing options...
iNow Posted December 21, 2007 Share Posted December 21, 2007 Yeah, I understand, but don't read into questions. You'll make errors. Look at the variables given, and work with them specifically. Don't start assuming winter and heat transfer and system energy and what season it is and what phase the moon is in and how many children you have and whatever else... The question said: You have some water and you stir it. Will it get warmer, cooler, or remain the same as a result of that stirring. KISS. Link to comment Share on other sites More sharing options...
MrMongoose Posted December 21, 2007 Share Posted December 21, 2007 Ok then, the answer is "Not enough information"- Isn't that usually d) in 4th grade multiple choice questions? I'm sure he'll get the answer by posting the thread in more than one section though Link to comment Share on other sites More sharing options...
swansont Posted December 21, 2007 Share Posted December 21, 2007 Yeah, I understand, but don't read into questions. You'll make errors. Look at the variables given, and work with them specifically. Don't start assuming winter and heat transfer and system energy and what season it is and what phase the moon is in and how many children you have and whatever else... The question said: You have some water and you stir it. Will it get warmer, cooler, or remain the same as a result of that stirring. KISS. Yes, KISS. One has to assume that the ambient temperature is the same, and that invisible elves are not dropping ice cubes into the mug, and that it's not sitting on a hot plate, etc. i.e. it's not a trick question. The question is "What is the effect of the stirring?" iNow's first response is appropriate. Remember this is HW help, and the goal here would be to point/lead drsckng3 to the correct answer, but not just blurt it out. Link to comment Share on other sites More sharing options...
thedarkshade Posted December 21, 2007 Share Posted December 21, 2007 If I stirred the water in the beaker vigorously for 3 minutes, will the temperature of the water increases, decreases or stay constant? Water is made up of molecules too, is it? And what happens when molecules hit each other? [hide]They generate heat, right! So the temperature increases. While stirring the water, you are increasing the kinetic energy of the molecules, and with the increase in kinetic energy, the probability that molecules will hit each other increases too. And as the hits of molecules are grater when you stir water, then hits generate energy, and that causes the increase in temperature.[/hide] Link to comment Share on other sites More sharing options...
swansont Posted December 21, 2007 Share Posted December 21, 2007 darkshade, I've edited your post (added spoiler tags). Please note what I had just posted, since you may have been composing your post before it arrived: in the HW forum, it is not proper to just give the answer. Let the poster try and figure it out from the hints, and they will probably learn more. Link to comment Share on other sites More sharing options...
iNow Posted December 21, 2007 Share Posted December 21, 2007 Ok then, the answer is "Not enough information"- Isn't that usually d) in 4th grade multiple choice questions? If I may be so bold, you clearly understand some higher level stuff, but you've completely missed the mark on this simpler question, and your answer is wrong. It's probably not appropriate to "help" others with the answer to their questions when you, yourself, don't know what it is. The answer is NOT "there isn't enough information." There IS enough information. Link to comment Share on other sites More sharing options...
thedarkshade Posted December 21, 2007 Share Posted December 21, 2007 darkshade, I've edited your post (added spoiler tags). Please note what I had just posted, since you may have been composing your post before it arrived: in the HW forum, it is not proper to just give the answer. Let the poster try and figure it out from the hints, and they will probably learn more. OK swansont, I'm sorry, I didn't know about this. And thanks for info... Link to comment Share on other sites More sharing options...
MrMongoose Posted December 21, 2007 Share Posted December 21, 2007 I wasn't so much trying to answer the question than to help the OP understand why the answer is what it is. If we blindly tell him that the end result of stirring a fluid is a warmer fluid, then he might make the error of stirring his cup of tea in a field in siberia and expecting that to be a magical way to ensure his tea doesn't cool down. More accurately, I'm being awkward because he posted the thread twice. Link to comment Share on other sites More sharing options...
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