Pierratos T., Koltsakis E., Polatolgou H.. «Teaching materials’ properties to K-12 students using a sensor board», Materials Education, edited by M. Marinho Patterson, D. Dunham, E. Marshall, J. Nucci (Mater. Res. Soc. Symp. Proc. Volume 1233, Warrendale, PA, 2010. DOI: 10.1557/PROC-1233-PP04-27.
Scratchboard is connected to a computer through a serial-to-USB cable that comes together with the board. The communication protocol is the RS-232 and the transfer baud rate is 38.4k. The connection between Scratch and Scratchboard is realized using sensing blocks. Sensor value blocks give readings ranging from 0 to 100 or ranging from 0 to 1023 if the user prefers to read raw 10-bit data . These values can be used to control graphic effects or can be stored in a log file.
In a stanchion we placed a steel bar with 30 cm length and 5mm diameter (Figure 1a).
Alternatively we used horseshoe bars of the same material (aluminum) and different thickness (3mm – 8mm) (Figure 2b) or the same thickness (3mm) and different material (copper – aluminum) (Figure 2c). In all cases one of the ends of the bar was placed above a candle flame. The rate of combustion should remain constant for all the experiments in order to provide heat at a constant rate. Along the bars thermistors were placed, connected with Scratchboard through alligator clips. As the bars were heated, the resistance of the thermistors was raised and their values were recorded. As these values are in arbitrary units; we used a digital thermometer for calibration.
According to the level of the students we addressed the Scratch’s interface differently. For elementary level students a bar was shown, with its color changing from point to point according to the chance of the temperature. For secondary level students graphs were provided that presented the change of temperature versus time (Figure 2).
Students realize the setting presented in Fig. 1a and start the measurements. Data collected for about 40 minutes are presented in Fig. 3.
The heating of the bar’s end is terminated at the moment that the temperature of the nearest sensor reaches its maximum (blue line). It is obvious in Fig. 3 that the temperature acquired at various points of the bar depends on their distance from the heating source. The closer to the source they are, the higher their temperature. It is also obvious that, for bar points far from the heat source, the temperature continues to increase, even after the interruption of heating (energy offer), due to the heat conduction from the hotter end to the cooler end of the
bar. Finally, during the cooling process, curves are compatible to Newton’s law of cooling. Students then realize the setting seen in Fig. 1b. Data collected for 40 minutes are presented in Fig. 4.
From Fig. 4, we can observe that the copper bar reaches faster higher temperatures than the aluminum bar, because of its higher thermal conductivity and lower heat capacity. Finally, students constructed the setting presented in Fig. 1c and started the measurements. Data collected for about 15 minutes are presented in Fig. 5.
Two phenomena can be distinguished in Fig. 5: a) because the thicker bar has a larger thermal conductivity, its temperatures increases more rapidly (at least in the beginning), and b) due to its bigger mass, the thicker bar’s heat capacity is larger than the thinner bar’s, resulting in a higher final temperature for the thinner bar. The graphic representations that came out are in very good agreement with results of simulations , , and they provide the chance to discuss the laws about the phenomena through inquiry based hands on activities.
It is quite obvious that this setup can provide an accurate measurement of the physical quantities involved after the thermistors’ calibration. In addition the low cost apparatus offers the chance to all students in a science class to study a law of Physics by participating in such a hands-on activity. At least in Greek schools, students usually just watch their teacher performing a high accuracy measurement experiment, using an expensive data acquisition system.
Data acquisition systems provide a powerful tool for measuring and presenting online various physical quantities in school science laboratories. As these systems are in general quite expensive and sophisticated, the use of Scratchboard and Scratch could provide an alternative solution for most schools’ laboratories. According to our experience, the appropriate use of such a system amplifies the possibility for students to be engaged in the learning process through programming, inquiry based and hands-on activities. Technically speaking, the sensor board can measure several physical quantities simultaneously and the powerful user-friendly software makes the presentation of the data as well as their processing easy. There is no doubt that the proposed system cannot totally replace the specialized data acquisition systems in upper secondary schools, where the students do have to make precise measurements. But it could be used in a very promising way in lower secondary and in primary education, where sophisticated data acquisition systems usually do not exist. This way would alter students’ interest about science and laboratory activities.
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