SCHOOL PHYSICAL EXPERIMENT Promoted by Digital Photographic Camera and Computer

Transcription

1 European International Journal of Science and Technology Vol. 3 No. 8 October, 014 SCHOOL PHYSICAL EXPERIMENT Promoted by Digital Photographic Camera and Computer Juraj Slabeycius Department of Chemistry and Physics Faculty of Education Catholic University in Ružomberok Nam. A. Hlinku 56, Ružomberok Slovakia Daniel Polčin Department of Informatics Faculty of Education Catholic University in Ružomberok Nam. A. Hlinku 56, Ružomberok Slovakia Corresponding Author s: Prof. Juraj Slabeycius, PhD. juraj.slabeycius@ku.sk & As.Prof. Daniel Polčin, PhD. daniel.polcin@ku.sk 115

2 European International Journal of Science and Technology ISSN: Abstract Actual paper is focused on the use of new observational and experimental methods in the physical laboratory experiments. This is an example of the utilization of the current digital photography in cooperation with computers and computer-supported experiments. We point to the possibility of eliminating the need for photographing objects by illumination with "flashes in the dark" with the classical use of stroboscope. Modern digital photographic devices allow so called "sequential exposure", which we successfully used for physical observation of fast moving objects and measurement of e.g. their path, speed and time of movement. The record of Figures in "sequential exposure" helped us create a sequence of several frames at a single shutter press in a rapid succession at specified time intervals of fractions of seconds, which are not measurable objectively by a stopwatch. Thus we eliminated a relatively large subjective error associated with a reaction time of a person. Technically well-defined time interval between two positions of the object and objective determination of its actual position in the made photos are the basis of our observations and physical measurements of parameters of different types, e.g. mechanical movements. Physical observations and measurements were also qualitatively and quantitatively analyzed and evaluated by means of video sequences made by digital photographic equipment. The video sequences were computerprocessed, using programs promoting physical experiment, resp. intended for video analysis of the made records. Key words: digital photography, physical phenomena, sequence exposition, video sequence. Foreword The problem of observation or measurement of physical quantities describing quickly moving objects was in the past solved most frequently with the use of a stroboscope. It is a device to reach a continuous action perception, when the individual and quickly moving phases of action are eye-watched, the mentioned principle is utilised e.g. in cinematography. Stroboscope enables to observe the action in any concrete phase within quick periodical actions as well as to slow them down. Stroboscope demonstrations are comfortable to excercise by a flashing stroboscope, where the flashes are produced by a discharge lamp and their frequency may be altered by an electronic device. The flashing period is a few microseconds, therefore the observed object appears sharp even at quick motion. If a periodically moving object (rotating etc.) is illuminated by light flashes at the frequency f z of the flashes equal to the frequency f p of the periodical action, the observed action appears to stop. If the flashes frequency is an integral multiple of the observed action frequency, tj. f z = n. f p, the object is illuminated n- times during a period and an observer perceives n different object positions. If the frequency f z does not differ substantially from the frequency f p, the object appears to be in a slow motion and the nature of movement during all the period can be observed. 116

3 European International Journal of Science and Technology Vol. 3 No. 8 October, 014 Figure 1: A classical stroboscope with an option to set up the flash speed and intensit with potentiometers. Colour shades: blue, yellow, red, black, white. Modern flash stroboscopes are digital and utilised in technical environment for an exact measurement of revolutions, checking of engines, kog wheel systems, centrifuges, generators and other engine systems. In the field of medicine, the stroboscope effect of flashing light is employed to ensure to keep e.g. a 4 hour non-sleep period with a patient. The stroboscope effect is also essential at the discos, where it becomes a part of the perceived rhythm and overall social ambiance. Figure : Party stroboscope Figure 3: Scanned periodical movement 117

4 European International Journal of Science and Technology ISSN: In physics, the stroboscope effect is utilized e.g. to observe a steady and steadily accelerated move- or to observe the ment of objects, to demonstrate the law of dynamics conservation at objects collisions, object movement in the homogeneous gravitation field of Earth /free fall, horizontal throw/. An object in the dark is illuminated by a stroboscope with a given frequency and an image is taken by a camera at a permanent shutter or relatively long exposure period. Figure 4: Free fall and horizontal throw Sequence exposition Present digital photography provides us with substantially better observation and experimental condithe illumination with tions. It eliminates the need of the observed objects photographing and measurement at e.g. flashes in the dark, with the classical utilisation of stroboscope. Thus it enables independent work in a single laboratory at daylight illumination of several simultaneous working groups and with the utilisation of today relatively widely spread digital photography devices, there is possible a following, continuous current analysis of the photo images on LCD monitors and primarily on computer monitors. Physical observation of moving objects and measurement of their e.g. trajectory, speed or movement time can be carried out by an images record in the mode of sequence exposition. The aim is to create a quick sequence of several Figures 118enis118 press of release, with an exactly set time of intervals in split second. The mode of sequence exposition - the frequency of Figures (number of Figures in 1 s) can be set 118enis necessary e.g. to or 3, whereas the number of potential Figures depends of the quality (JPG, stan- us with an exact dard etc.) and the memory card capacity. The frequency of sequence exposition provides time interva l between Figures, e.g. with f = 3 s -1 it is 1/3 s. This fixed time interval eliminates the need to use a stopwatch and also subjective errors when measuring the times of objects motion on individual tramoment and thus the jectories parts. Recorded images enablee an exact location of moving object in a given measurement of a run trajectory lap. The exactly determined time interval between two positions of object and an objective determination of its current position are essential for observation and physical measurements of parameters of different types of e.g. mechanical movements. The example of the above-mentioned application of digital camera with the mode of sequence expo- at the Earth sur- sition at the physics laboratory practice is e.g. the measurement of acceleration of gravity face. There are several possibilities to determine g = 9,81 m. s -.

5 European International Journal of Science and Technology Vol. 3 No. 8 October, 014 l 1. Mathematical pendulum: T = π, where l is a measured pendulum length and T is a pendulum g period determined by e.g. a stopwatch. 4π l g = T. Reverse physical pendulum: T r = l r π, where lr is so called reduced length of the physical pen- g dulum, determined experimentally by a series of measurements, and T r is a corresponding period determined graphically by period measurements at different pendulum lengths. 4π l g = T r r 3. By the sequence exposition, the acceleration of gravity can be exactly measured from the free fall trajectory, following the relation 1 s = gt s g = t where t = 1/3 s is the time interval between the first and the second read position (at the frequency of sequence exposition e.g. f = 3 s -1 ), and s is the distance of these positions. At this measurement, the use of stopwatch is eliminated and it can also be carried out on a short trajectory, which is impossible with a manually operated stopwatch (as in 1 second, an object at the free fall moves along a trajectory of about 5 metres length!). 119

6 European International Journal of Science and Technology ISSN: Figure 5: Free fall of a table tennis ball 10

7 European International Journal of Science and Technology Vol. 3 No. 8 October, 014 Figure 6: Free fall of a wooden ball With a change of ball weight, the free fall speed independence from the weight of object can be proved. v = gt Using a digital camera, a well-known laboratory practice called Experimental observation of mutual transformations of mechanical energy forms (Physics for the 1 st year of grammar schools) can be carried out: Figure 7: The experiment scheme

8 European International Journal of Science and Technology ISSN: The complicated determination of No. ball speed, gained by No.1 ball impact, following the relation v = d g H by a measurement of distance d from the diffusion of several impact points of No. ball on a surface, is replaced by a sequence exposition to determine the flown distance s of No. ball in the horizontal direction in the above-mentioned time t = 1/3 s, between the first and the second read position s = vt s v = t Figure 8: The horizontal throw of a ball Figure 9: The measurement of ball speed in a horizontal direction In a similar way the experiments can be simplified and specified by elimination of stopwatch usage at e.g. the laboratory practice called: Experimental observation of ball movement kinematics on an inclined and horizontal plane (Physics for the 1 st year of grammar schools): 1

9 European International Journal of Scien ence and Technology Vol. 3 No. 8 October, 014 Figure 10: The experime mental scheme Video-sequences The above-mentioned experimen ents carried out with the sequence exposition ccan be analyzed both qualitatively and quantitatively, using ng video sequences made by a digital camera era and processed in a computer using programs supportingg physical experiment resp. making a video aanalysis of the ready records. ables a simple control and data transmission in into E.g. the program Easy Vid enab MS Excel. Laboratory set Coach 5 provides pr a more sophisticated both software andd hardware support to physical measurements and observations ns. Figure 11: Free fall of a ball, processed pr by Coach 5 program Figure 1: The correlation off ball b trajectory and elapsed time during a fre ree fall, processed by Coach 5 programme 13

10 European International Journal of Scien ence and Technology ISSN: Numerous programs enabling to view individual video sequence Figures, e.g..g. Quick time Player, BSPlayer, Viana, provide us with similar lar possibilities to analyze the video sequences. Experiment realization A ball falls down along a board. d. Its fall is scanned by a digital camera. The scan canned video sequence with the falling ball is transferred intoo a computer. It can be viewed in some of the ab above-mentioned programs. By analyses of individual image ges, the ball positions in corresponding time mooments can be determined. These positions are marked on the t board, along with the time periods from thee beginning b of the fall. Then the distances of individual positio tions from the initial position are measured and tthe length of the ball trajectory from the beginning of the fall ll to the individual marked positions is determined ed. Figure 13: Prepar ared videomeasurement of a free fall Subsequently, the students use the th data to draw a graph of relationship between en the trajectory length and the elapsed time. The graph shows a steady acceleration of the movement. With the he measured data the time of the fall beginning, the time of the th last scanned position and its distance from the th initial position, the - acceleration of gravity g = 9.81 m. s is calculated. Figure 14: A ver ertical throw processed by Coach 5 14

11 European International Journal of Science and Technology Vol. 3 No. 8 October, 014 Figure 15: An inclined throw processed by Coach 5 Conclusions It can be said that a digital camera, with an option of the sequence exposition and video sequence, can be broadly utilised in physical demonstrational and laboratory experiments. It simplifies and specifies the measurements especially when observing rapid processes. It enables independent work of several simultaneous working groups in a single laboratory and there is a possibility of an instant analysis of the photo images on LCD monitors and on PC monitors. References [1] HORVÁTH, P. - ŠEDIVÝ, M.: Analýza mechanického pohybu videomeraním. In: Aktivity vo vyučovaní fyziky (An analysis of mechanical movement by video-measurement). Bratislava: FMFI UK 006. (in slovak) [] HENNINGES, H.: Nový základný kurz fotografie. Cesta k dokonalej fotografii. (New basic course of photographing. Ways to the perfect photo) Bratislava: Ikar 00. (in slovak) [3] KAŠPAR, E. VACHEK, J.: Pokusy z fyziky na středních školách. (Physical experiments at the high schools.) Praha: SPN (in czech) [4] VACHEK, J. a kol. : Physics for the 1 st year of grammar schools. Bratislava, SPN (in slovak) [5] ČERNAK, I.: Tvorba a spracovanie videa. In: Odborný seminár - Využívanie multimédií a informačných komunikačných systémov vo vyučovaní informatiky, Ružomberok 1.. februára 007. (in slovak) 15