Reel Joule

The story

James Prescott Joule, English physicist, was one of the greatest scientists of the nineteenth century, but, as often happened in those days, had another job in fact worked in his father’s brewery. He had a workshop in the factory where he did his experiments, and when he sold it with the money he had obtained a considerable economic tranquility that was able to devote himself entirely to physics. Study at home and for three years as a teacher was the eminent chemist John Dalton, then seventy. Dalton passed to Joule his great love for science and his passion for the accuracy of the numerical data on which to base the laws and scientific theories. Unfortunately Joule studied little mathematics and this prevented him, in the last years of his life, to give the most significant contributions to physics. The concept of energy, in the time of James Prescott Joule was limited, in addition to the electric, these three types of energy: potential, kinetic and mechanical. The first is a certain energy that a body possesses due to the fact that it can perform a task, the second is an energy that a body possesses due to its motion, and the third is the sum of the kinetic energy plus the potential energy, which remained constant if it refers to a closed system. Moreover, the heat was considered as a substance imponderable and conservative, called heat flow, which passed from the body warmer to the colder body and the passage is interrupted when the two temperatures taking the same value. Joule began to work on the concept of heat when he noticed a thread in which electric current is passed warming. This resulted senseless since, as has been said, the passage of heat occurred only in the presence of two bodies having different temperatures: in this case, therefore, would not have noticed no change in temperature. In addition, the theory of caloric fluid was beginning to have other discrepancies with what was observed, in fact, another famous scientist, Thompson, noted that the friction could generate an indefinite amount of heat without any apparent passage of heat flow. All of this brought to mind the idea that the Joule heat could be a form of energy. Joule, also supported by these new observations, drew up an experiment, able to demonstrate that heat was a form of energy, built a machine, which in honor of him was called Reel Joule.

The famous experiment

The weights, placed at a certain height, are made to descend in free fall by moving the pallets that are inside the insulated container closed and perfectly: they put in motion so the water inside the container. Joule see that the potential energy of the initial weights did not equal the final kinetic energy, but there was a small amount of energy. All this was against the law of conservation of mechanical energy. The scientist was in mind then inserting a thermometer into the container and try again repeating the experiment several times consecutively the fall of the weights, so as to increase the amount of energy, he realized that there was a slight increase in temperature, sensing that the missing energy was transformed into heat gained, then subsequently the water. Thanks to this experiment, Joule pote state that: “the heat is a form of energy that said thermal energy is transferred from one body to another by virtue of the temperature difference and can be exchanged, with a defined ratio, with the other forms of energy. “The value of the relationship between work and heat, found experimentally by Joule at the time, was calculated as 4.18 J / cal.

Our experience

The calorimeter

The building of the reel Joule involves an in-depth knowledge on the theory of heat and have embraced the principle of the calorimeter, a tool that allows you to measure the flow of heat between two bodies, one of whom know exactly its properties to define with them the characteristics of the other. Before proceeding with our project, so we spent several hours discussing the concept and the definition of specific heat of water equivalent of the calorimeter. The process, by which you can determine the amount of heat that a body acquires or sells, is as follows: 1. Far heat and bring to boiling water in a container, plunging even the body, where you know exactly the specific body and saw that the temperature was equivalent to that of water, then you’ll need to check whether the theory of heat is agrees with the experiment. And is chosen as the temperature of boiling water because we know that, in the transition state, it remains constant and therefore allows us to know exactly the temperature of the immersed body. 2. In a calorimeter, heat insulated, you will pay a certain amount of water at room temperature, and is measured with a thermometer, this will be the water that will acquire the heat lost from the body immersed in water at about 100 ° C. 3. When the water mass to warm up and come to the boil, take the body, which is usually one or two metal bars, and dives into the water container at room temperature, close the container, puts the thermometer, you measure the elevation of the water by taking the highest value that is reported. Through the following formula is obtained by the heat lost from the body and that purchased by the water in an ideal experiment is equivalent to: Q = Q succumbed purchased body body m x Cs x Dt = m water body water x Cs x At water Where: · m indicates the mass; · Cs is the specific heat, that is the quantity of heat required to raise the temperature of a degree of a kg of the material; · Dt the difference between the initial and final temperature of a body. We performed four experiments on calorimeter and following are the values and calculations relating to them.

1st Experience

Note: we used two fingers as the body of iron. Data: m = 136 g iron CS iron = 0.108 cal / g Do you iron = 99.8 ° C Teq = 26.2 ° C You water = 22.6 ° C m water = 370 g Cs water = 1 cal / g Substituting these values to the equation: Q = Q succumbed purchased body body m x Cs x Dt = m water body water x Cs x At water 136 gx 0.108 cal / gx (99.8 – 26.2) ° C = 350 gx 1 cal / gx (26.2 – 22.6) ° C (Q sold) 1081 cal = 1260 cal (Q purchased)

2nd Experience

Note: we used two fingers as the body of iron. Data: m = 136 g iron Do you iron = 99.4 ° C Teq = 21.4 ° C You water = 18.2 ° C m water = 370 g Substituting these values to the equation: 136 gx 0.108 cal / gx (99.4 – 21.4) ° C = 370 gx 1 cal / gx (21.4 – 18.2) ° C (Q sold) 1146 cal = 1184 cal (Q purchased)

3rd Experience

Note: we used two fingers as the body of iron. Data: m = 136 g iron Do you iron = 99.8 ° C Teq = 22.6 ° C You water = 19.6 ° C m water = 370 g Substituting these values to the equation: 136 gx 0.108 cal / gx (99.8 – 22.6) ° C = 370 gx 1 cal / gx (26.2 – 21.8) ° C (Q sold) 1133 cal = 1110 cal (Q purchased)

4th Experience

Notes: We used two fingers as a body of aluminum. Data: m = 110 g aluminum Aluminum Cs = 0.215 cal / g You are aluminum = 100.0 ° C Teq = 26.2 ° C You water = 21.6 ° C m water = 370 g Substituting these values to the equation: 110 gx 0.215 cal / gx (100 – 26.2) ° C = 370 g 1 cal / gx (26.2 – 21.6) ° C 1735 cal = 1702 cal

Conclusions on the work done by the calorimeter

After doing the calculations, in the first two experiments, we found the results unlikely because the heat gained by the water can not be greater than the heat lost from the body otherwise it would violate the principle of conservation of energy. It would even be reasonable to think that the amount of heat should be purchased, albeit slightly, less than that sold Whereas the dispersions of the container. So he sought and possible error factors, those that could result in a significant error: · The rust layer of the two iron bars that modify the value of the specific heat. It was solved by trying the aluminum bars that do not give any particular problems typical of iron; · Too much air in the calorimeter, in fact there is more more air increases the heat dissipation. It was solved by filling the container with water to the maximum in order to minimize this dispersion · Using the same thermometer for the two containers: first by immersing in boiling water and a little later in the calorimeter, most likely, has released its heat to the Body then going to distort the result of the experience.

The reel Joule

The project is a reel from the difficulty in fully understand the concept of heat as a form of energy. And then you decided to retrace the same path made by Joule, recovering from his famous experiment with the idea of maximum build in small size, the reel in its original form. During the construction we ran into some problems with the reasoning and the ‘everyone’s help we were able to overcome. Below list all the problems had during the design phase and subsequent construction: · The fixed blades have been difficult to mount both for the necessary precision in the position them inside the container and both for the difficulty in working in a small container, also we had to put them in so they do not interfere in the work of the vanes. · The increase in temperature and very minimal so we looked for a system with pulleys and shaft so that it would create the least friction possible not to distort the result. · The availability of materials and labor was another problem, because the reel and a machine that requested items are not easy to find as the brass rod, which was to have a very precise shape and diameter, the pulleys were not good condition but thanks to the work of Professor Arfini we were able to put them back on their feet and are now fully functional. The building of the reel has been carried out in this way: 1. We, first, set the two brass rods that served as support for the pulleys on a pedestal 2. Choosing the appropriate container for this project, small and insulated, we have designed and sized the “system palette fixed” bearing in mind that had to be made from a material that is easy to work on and good thermal conductor 3. Meanwhile, in parallel, we tried two pulleys that were a useful diameter in our experiment and that they had a friction with the terminals too high 4. We started, then, to construct the fixed blades, anything but simple, with the slats of copper, welded together and positioned at a determined distance; 5. While the construction of the palette progressed we adapted a brass rod as the core of the reel, so that we did too much friction tapered tip and built a sort of basin that we pasted into the bottom of the container 6. Finished the construction of fixed blades, we isolated the container by placing around it a foam and then inserted into a larger container; 7. We continued with the construction of floating palettes, these much more easy to make, and then welded them to the central rod so that it did not touch the moving blades fixed 8. Finally we connected via a wire, rod movement of the weights, 500 g each, mounted on pulleys. Now that we have finished the construction will proceed with the tests, either with water or with oil, aims to test the operation of our reel comparing ourselves with the theory.