Science Buddies: "Ask an Expert"

Hello, I did this project, https://www.sciencebuddies.org/science- ... p057.shtml .
Results Fastest to Slowest: Every 5 Minutes, Starting at a room Temperature of 68F
Ice-waterbath: 42F,36F,32F
Ice-only bath 46F,42F,41F
Freezer Compartment 56, 56, 52
Refrigerator 62, 58, 58
No salt was used in this experiment.
By the way, I find these results of the freezer and refrigerator a little odd.It SHOULD be okay right since it was staying constant for that time?

I am familiar with theses terms:
Conduction
Convection
Evaporation
Radiation

My main problem is I'm not sure how the Ice-waterbath is the fastest. It would really help if you would respond quickly, thanks.

I just answered a similar inquiry for another student. I think you will find the information on this web site helpful in explaining why ice-water should work faster:
http://www.eduplace.com/kids/hmxs/g6/we ... t2cc.shtml

If you still have questions, stop by "Ask An Expert" again.

edneu3 wrote:I just answered a similar inquiry for another student. I think you will find the information on this web site helpful in explaining why ice-water should work faster:
http://www.eduplace.com/kids/hmxs/g6/we ... t2cc.shtml

If you still have questions, stop by "Ask An Expert" again.

Thanks, but what about my results? Is it possible that they stayed constant for that time?

I'm pleased that you are looking at your data critically. While it is certainly true that experiment always beats theory when there is a conflict, there are still many ways that experimental data can be wrong. Critical thinking is one of the roots of the scientific method.

I agree that some of your data points look odd. I assume that the values you gave were each an average of three measurements on three cans, so did the three agree with each other? I would expect some differences because of several factors such as the repeatability of measurements made by the thermometer, small differences in the placement in the cans in the cooling environment, differences in the exact placement of the probe within the fluid. If the spread in the three values were of order 2 degrees, then the error in the average might be about 1 degree, which would go a good deal of the way to explaining the observed peculiarities. Also, did you carry on making measurements until you got at least three that were the same before deciding that the cans had stabilized to their final temperatures? I'm surprised, for example, that the ice-only data stabilized at 41 F; given enough time, surely it would have gotten close to 32 F, the temperature of the ice. I have similar concerns about the refrigerator and freezer data; my guess is that it would take a lot longer than 15 minutes for the sodas to reach their final temperatures. Looking at the attached graph (PDF) I think that if there were error bars of, say +_ 1 F and if you had continued taking data for half an hour, then the graphs would have ended up looking pretty reasonable.

The only thing I can think of in addition to John's theories is: Did you remove the cans from the fridge to make the measurements? If so, were you careful to handle them with something well insulated? Because the heat of your hands is enough to cause some variation in the temperatures.

The ice water bath is the fastest cooling method since more cold molecules are in contact with the surface of the can than any of the other cooling methods. For example, even though ice itself is colder than ice water, the pieces of ice only come in contact with a relatively small fraction of the can's surface compared to the water. Also, even though cold air also comes in contact with the entire can's surface, it has fewer molecules per area than water so it too will take longer. Hope that helps.