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For my research project, I was inspired by phase change experiments using water from solid to liquid forms, as can be found in our physics book Physics: Principles with Applications, by Douglas C. Giancoli, and Turning the World Inside Out by Robert Ehrlich. Based on a suggestion from my friend Sarah Chan, I decided to conduct my own phase change experiment. Other substances, instead of water, can be turned into liquid form, and the substance I chose in place of water was cheese. I also decided that I would induce the phase change with heat not from a flame, but from a microwave. At the beginning, I had one objective--to find the work done on different types of cheeses by a microwave. Realizing the proportional relationship between MW and BG (More Work = Better Grade), I also decided to use this experiment to find something IÕd only learned about recently--the Latent Heat of these cheeses as well.
After deciding what I was going to do, I did further research, finding information about microwaves and their power outputs, and also observing other heat and phase change experiments online at several college Laboratories. Armed with our IB Physics II text (Physics: Principles with Applications, by Douglas C. Giancoli) I found two formulas that would give me what I wanted: P = W/t for finding the Work done on the cheese by the microwave and Q = ml for finding the Latent Heat of each cheese. In the first equation, I knew that P = 900 Watts, and that I could find t. Knowing those I could easily find W (Work). In the second equation, I knew the mass m for each cheese sample, but I was unsure of what to use for Q to solve for l until I realized that Q is also in Joules, like Work, and I could substitute W for Q. Therefore, using P = W/t, with the Power of the microwave in Watts, and the Time in seconds, I was able to calculate W, in Joules. W, the energy expended during the phase change, can then be substituted for Q in the equation Q = ml, and using the mass m, and the Energy found with the equation P = W/t, I am able to find the Latent Heat l for each kind of cheese.
After creating my procedure--I would melt each sample of cheese and watch it until it began to melt, noting the time of each cheese--I set out to purchase my supplies. At the deli of the local Safeway, I bought two slices of every cheese they had, which was only 7, in the end. Wanting to round out the desired sample set of 10 cheeses, I wandered to the speciality cheese section, and purchased soft cheeses. This created on accident another hypothesis to be pursued. I hypothesized that the soft cheese would melt faster than the hard cheese. I found three soft cheeses of different softness and textures, and headed home. My sample set of cheese was made up of: Cottage Cheese, Longhorn Colby, American Yellow, Mild Cheddar, Berganthaler Natural Swiss, Alpine Lace Swiss, Provolone, Muenster, Cream Cheese, and Brie.
I used an ordinary household
microwave with a power output of 900 watts to heat the cheese and induce
phase change from solid to liquid. I timed how long it took for each cheese
to begin to melt, as I was not concerned with the entire sample of cheese
to be melted all the way through. The raw data table that I collected during
the experiment is show below. The table lists the name of each sample of
cheese, the time (in seconds) it took to melt the cheese, and the mass
(in kilograms) of the sample melted in order from the smallest mass to
the largest mass.
With this raw data, I was able to find my objectives--the work done on each sample of cheese by the microwave, and the latent heats for each sample of cheese. My calculations are attached, and a table with the sample name, Work (in joules) done
by the microwave on that sample, and the Latent Heat (in kg/J) of
the sample is shown on the next page.
With the objective found,
I endeavored to analyze the data using graphs. This first graph shows the
relationship between the mass of the sample and the time it took to melt
Not surprisingly, the time it took to melt the samples is longer when the mass is larger. There are a few exceptions to this rule--Sample #8, the Brie, took less time to melt that the proceeding samples, which is probably due to the fact that it was the softest cheese of all the samples. The two samples that took the longest to melt are also soft cheeses, but the texture and thickness of these cheeses could explain the reason it took so long to melt. With Sample #10, the Cottage Cheese, which would seem likely to melt first, it is possible that the curds melt more slowly because they are in the whey. With Sample #9, the Cream Cheese, the thickness of the sample is most likely why it took so long to melt.
This second graph shows the
relationship between the mass of the sample and its Work.
This graph is nearly identical to the mass v time graph, as there is an obvious linear relationship between the mass and the Energy, or Work used to melt it. Once again, Sample #8 is an exception to the trend, reason being its soft texture, and Sample #9, Cream Cheese used the most energy to melt because, as pereveiously noted, it was the thickest sample of cheese melted.
The third graph shows the relationship between the Mass of the sample and the Latent Heat of the cheese, and it attached on the next page. Please refer to it for the following discussion. The computer, for some reason, did not like that graph and would not allow me to put it on this page for discussion, although I tried and tried and tried. This graph offers the most opportunity for analysis, because there is no linear relationship between the mass of the sample and the Latent Heat of each cheese. For example, Samples #6 and #7 , the Alpine Swiss and Provolone, respectively, have lower Latent Heat than Sample #8, the Brie. One reason this may be true, may be because the Alpine Swiss and Provolone may have been designed with a texture that allows it to melt with more ease than the Brie. The Brie may be a soft cheese, but itÕs texture is possibly made to withstand melting up to certain temperatures.
With this hypothesis--that certain cheeses are made to melt at lower temperatures than others, it is significant to note that the American Cheese, Sample #1, has the lowest Latent Heat of the hard cheeses. Cottage Cheese, Sample #10, has the lowest Latent Heat of all, most likely because of the whey that is with the curds. The watery whey allows the cheese to melt at a lower temperature than the other cheeses. Significantly, the two highest Latent Heats are that of Sample #9, Cream Cheese, and Sample #5, Longhorn Colby. Colby has a high Latent Heat, possibly, because it is most often used as a solid, instead of as melted, unlike Cheddar or American Cheese, and Cream Cheese would have the highest Latent Heat because of itÕs texture. ItÕs meant to stay solid, and is therefore resistant to melting at lower temperatures.
In conclusion, I could call this project a success, because I did find my objectives. I found the Latent Heat and Work for many different kinds of cheese. My hypothesis about soft cheeses melting faster than hard cheeses turned out to be incorrect, but this may well be because soft cheese is meant to stay soft even in warm temperatures, whereas most hard cheese is melted, and a low Latent Heat allows for faster melting. This project, which I at first thought laughable, does have some scientific basis, and the Latent Heat for different cheeses can correspond to common sense assertations when placed under analysis.
Ehrlich, Robert. Turning the World Inside Out. Princeton
University Press. Princeton, New Jersey. 1990.
Giancoli, Douglas C. Physics: Principles with Applications 3rd
Edition. Prentice Hall. Englewood Cliffs, New Jersey. 1980.
Kittel, C. and H. Kroemer. Thermal Physics. W.H. Freeman & Co.
San Fransisco. 1980.
Zemansky, Mark W. and Richard H. Dittman. Heat and Thermodynamics.
McGraw-Hill Publishing Co. London. 1981.
<http://anvil.me.uh.edu/heatlab/htl.html> The University of
Houston Heat Laboratory. 1996.
<http://www.microwavenews.com> Microwave News (Newsletter). 1998.
http://www.madsci.org/experiments This is a website filled with fun experiments including ones dealing with cheese and heat, among others.
http://www.worc.ac.uk/departs/enuman/Staff/Rowland/UMS/enu/ENV101/lectures/Lecture01/Heat/HeatB.html This is a brief overview of latent heat.
http://www.science.urich.edu/~rubin/pedagogy/132/132notes/Heat.html A very very specific and helpful website about heat and temperature in general. It's like reading a physics book in translation.
http://www.futuresouth.com/~mhenders/physics/physics.html Physics lab experiments including ones about latent and specific heat, although they use water instead of cheese.
An actual serious scientific experiment that deals with melting cheese.