Površinska napetost in plavanje

magistrsko delo

Nina Košmrlj (Author), Mojca Čepič (Mentor)

Abstract

Poučevanje naravoslovja in fizike ni zgolj predelava tem iz učnega načrta, temveč tudi osmišljanje pridobljenega znanja in povezovanje s primeri iz posameznikovega vsakdana. Površinska napetost je pojav, ki je le v manjši meri prisoten v učnih načrtih za osnovno šolo, pa vendar ima velik pomen v naravi in vsakdanjih opravilih. Brez nje namreč nekatere živali (na primer vodni drsalec) in rastline ne bi živele na način, na katerega živijo sedaj. Vsakdanja gospodinjska opravila bi bila mnogo težja brez izkušenj o površinski napetosti vode in uporabi površinsko aktivnih snovi. Pa tudi zelo pogosti pojavi, kot sta na primer zvrhan kozarec vode ali pa nastanek kapljic, so neposredno povezani s površinsko napetostjo. V delu obravnavam nove eksperimente, ki še niso raziskani v celoti ali nasploh. Osredinim se na ukrivljenost gladine kapljevine in posledično nastanek posrednih sil med predmeti, ki plavajo na gladini, raziskujem plavanje ledene kocke v olju in za konec še povežem plavanje in vzgon s površinsko napetostjo na primeru ledu v kapljevinskem stolpcu vode in olja. Eden od učinkov površinske napetosti, s katerim se učeči se pogosto ne srečajo, je, da se zaradi plavajočega predmeta ukrivi gladina kapljevine. Kot posledica se zaradi površinske napetosti pojavijo posredne sile, ki težijo k zmanjšanju proste gladine kapljevine in se pokažejo skozi gibanje plavajočih predmetov. Med njimi namreč nastanejo posredne sile, ki povzročijo bodisi odboj bodisi privlak. Tako se dva predmeta, ki ju kapljevina moči, privlačita in enako velja za predmeta snovi, ki ju kapljevina ne moči. Če kapljevina moči predmet iz ene snovi in ne moči iz druge, se predmeta iz teh dveh snovi odbijata. Učencem je to znano iz izkušenj, da se kosmiči, ki plavajo na mleku, privlačijo in združujejo. V deloma polni posodi se premikajo proti stenam posode, v zvrhani, z izbočeno gladino pa proti sredini. Pri plavajočih kovinskih predmetih je opazen obraten učinek; v deloma polni posodi se premikajo proti sredini posode, v zvrhano polni pa proti stenam posode. V delu sem oblikovala aktivnosti z zanimivimi nalogami in eksperimenti, namenjene pridobivanju izkušenj in razumevanju pojava posrednih sil med predmeti, med katerimi sicer sile v splošnem ne obstajajo. V drugi seriji aktivnosti sem raziskala in oblikovala aktivnosti o plavanju ledene kocke med vodo in oljem. Podrobneje sem raziskala površinsko napetost med vodo in oljem, zopet preko aktivnosti. Koeficient površinske napetosti med vodo in oljem je v literaturi redkeje prisoten in zato s stališča raziskovanja bolj zanimiv. Kvalitativno sem opisala in primerjala površinsko napetost, ki nastane med kocko ledu iz destilirane, vodovodne in sladkane vode ter plastjo olja. Načrtno sem spremljala taljenje kvadrov iz zamrznjenih kapljevin različnih gostot. Primerjala sem položaj zamrznjenih kvadrov v odvisnosti od različne površinske napetosti v plasti vode. Ko se kocka tali, se okrog nje oblikuje plast tekoče vode, kocka pa ostane prilepljena na plast vode pod oljem. Ob dodajanju površinsko aktivne snovi - detergenta, sem spremljala položaj kocke v tekočinskem stolpu, glede na gostoto kapljevine, iz katere je zamrznjena kocka. Zanimivo je, da vsi trije kvadri plavajo v plasti med vodo in oljem, vendar pa se ob dodajanju detergenta kvadra iz destilirane in vodovodne vode odcepita od vodne gladine in splavata na gladino olja, kvader iz sladkane vode pa ostane na plasti med vodo in oljem. Poiskala sem tudi najmanjšo koncentracijo sladkorja v zamrznjeni kocki, pri kateri kocka še splava na površino olja. V tretji seriji aktivnosti sem poskusila poiskati koncentracijo detergenta, pri kateri se bo ledeni kvader odlepil od površine vode. Zanimivo je, da se kvader ob postopnem dodajanju detergenta najprej obrne in šele nato splava na gladino olja. Iz tega primerjanja sem ocenila vrednost površinske napetosti na meji med vodo in oljem. Oblikovala sem naloge in poskuse, s katerimi bi učenci pojav lahko raziskovali sami. S pomočjo vseh aktivnosti bodo imeli učenci boljši vpogled v delovanje površinske napetosti in njenih učinkov ter pridobljeno znanje povezali z vsakdanom.

Keywords

površinska napetost;prosta gladina kapljevine;posredne sile;ukrivljenost gladine;plavanje;površinsko aktivne snovi;

Data

Language:	Slovenian
Year of publishing:	2022
Typology:	2.09 - Master's Thesis
Organization:	UL PEF - Faculty of Education
UDC:	53(043.2)
COBISS:	129214467
Views:	17
Downloads:	4
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Surface Tension and Floating
Secondary abstract:	Teaching science and physics is not just a talking about topics from the curriculum, but also making sense of the acquired knowledge and connecting it with examples from an individual's everyday life. Surface tension is a phenomenon that is only to a lesser extent present in primary school curriculum, yet it has great importance in nature and everyday tasks. Without it, some animals (such as the water strider) and plants would not live the way they do now. Everyday household chores would be much more difficult without experience about the surface tension of water and the use of surfactants. Even very common phenomena, such as an overturned glass of water or the formation of drops, are directly related to surface tension. In the work, I discuss new experiments that have not yet been fully or at all explored. I focus on the curvature of the liquid surface and the resulting indirect forces between objects floating on the surface, investigate the floating of an ice cube in oil, and finally connect floating and buoyancy with surface tension on the example of ice in a liquid tower of water and oil. One of the effects of surface tension that students often do not encounter is that a floating object bends the surface of a liquid. As a result, indirect forces appear due to surface tension, which tend to reduce the free surface of the liquid and manifest themselves through the movement of floating objects. Indirect forces arise between them, causing either repulsion or attraction. Thus, two object which the surfaces are wetted by the water attract each other and the same applies to two objects which the surfaces are not wetted. If a surface is wetted in one object and not in another, object then they repel each other. Students know this from experience, that corn flakes floating on milk are attracted to each other and come together. In a partially full container, they move towards the walls of the container, and in full one, with a convex surface, towards the center. The opposite effect is observed with floating metal objects; in a partially full container, they move towards the center of the container, and in an overflowing container, they move towards the walls of the container. I designed activities with interesting tasks and experiments aimed at understanding the occurrence of indirect forces between objects, between which forces do not generally exist. In the second series of activities, I researched and designed activities about the floating of an ice cube on the layer between water and oil. I explored the surface tension on this layer in more detail, again through activity. It is less common in the literature and therefore more interesting from the point of view of research. I described qualitatively and compared the surface tension that occurs between an ice cube made of distilled, tap and sweetened water and a layer of oil. I systematically monitored the melting of blocks from frozen droplets of different densities. I compared the position of the frozen cubes depending on the different surface tension in the water layer. As the cube melts, a layer of liquid water forms around it, and the cube remains stuck to the layer of water under the oil. When adding the surfactant-detergent, I will monitor the position of the cube in the liquid tower according to the density of the liquid from which the cube is frozen. Interestingly, all three blocks float in the layer between water and oil, but when detergent is added, the blocks from distilled and tap water detach from the water surface and float to the oil surface, while the blocks from sweetened water remain in the layer between water and oil. I found the minimum concentration of sugar in a frozen cube at which the cube still floats to the surface of the oil. In the third series of activities, I tried to find the concentration of detergent at which the cube will detach from the surface of the water. It is interesting that when the detergent is gradually added, the block first turns and only then floats to the surface of the oil. From this comparison, I estimated the value of the surface tension at the boundary between water and oil. I designed tasks and experiments with which the students could investigate the phenomenon themselves. With the help of all the activities, students will have a better insight into the operation of surface tension and its effects and will connect the acquired knowledge to everyday life.
Secondary keywords:	surface tension;free surface of the liquid;indirect forces;surface curvative;floating;surfactants;Fizika;Univerzitetna in visokošolska dela;
Type (COBISS):	Master's thesis/paper
Study programme:	0
Thesis comment:	Univ. v Ljubljani, Pedagoška fak., Poučevanje
Pages:	1 spletni vir (1 datoteka PDF (VII, 70 str.))
ID:	17070391