Stickin Tgether: Surface Tensin, Chensin, and Adhesin FRAMEWORK I. Scientific and Engineering Practices II. Crss-Cutting Cncepts III. Physical Sciences SKILLS/OBJECTIVES Explring water s ability t stick t itself and ther materials; seeing what amazing prperties this prduces; cnnecting these facts t everyday bservatins like water s meniscus, the ability fr bjects t flat n water, dew drps frming n plants, and the mvement f water frm rt t stem in plants. MATERIALS Water (1 galln?) 2 test tubes 15-20 Pipettes 15-20 pennies 20 small Dixie cups 5 larger glasses Rll f paper twels 15-20 paper clips Sap Oil, ethanl (1/2 galln each?) Fd dye NOTES The capillary actin activity shuld be re-visited at the end f the lessns t examine its prgress The first activity shuld be dne as a large grup, but the rest can be in smaller grups (3-5) kids with a club member. These activities shuld be accessible t all age grups
BACKGROUND Water is all arund us and is necessary fr every kind f life n this planet. Mst f yur bdy is made f water, and s is mst f the planet! There are sme really special and cl things abut water that make it unique. It is actually really sticky stuff, even thugh it desn t feel that way. It is able t grab nt itself better than a lt f ther material. When it sticks t itself, water becmes very strng and able t hld things. Have yu ever seen a bug walking n the water? The key idea here is that water sticks t things, especially itself, by grabbing and hlding n which can lead t incredible strength and the ability t wrk against ther frces. Activity # 1 Materials Hydrgen Bnding Nne Wrksheet Nne This is t prvide an intrductin t the idea f hydrgen bnding. Have each f the kids be an individual mlecule f water (r if they dn t understand that, maybe a part r piece f water?). Water likes t hang ut with friends, s everyne shuld try t hld hands (feet?) with as many peple as they can at nce! In water, this kind f hlding hands and feet is called a Hydrgen Bnd. Nw everyne is ging t be a different kind f liquid, like ethanl r il. These liquids dn t like hanging ut with ther peple as much, s everyne can nly hld hands with ne ther persn and put the ther hand behind their backs. Which f these liquids, water r ethanl/il, is strnger? If we were t thrw a stuffed animal n tp f yu, which grup wuld prevent it frm hitting the grund? Water is strnger because it likes t stick tgether!. Activity #2 Capillary Actin Paper Twel Race! Materials 2 test tubes 1 small Dixie cup filled with water 1 small Dixie cup filled with il 2 empty Dixie cups 2 pieces f twisted paper twel Fd dye
Wrksheet Nne This activity shws hw water may adhere t ther surfaces t wrk against the frce f gravity. This same principle, water s ability t stick t nn-water surfaces, is respnsible fr cncave appearance f water s meniscus. Mercury, n the ther hand, has little adhesive prperties, s the liquid in a thermmeter, fr example, frms a cnvex meniscus. Similarly, adhesin allws water t flw up small-diameter tubes, the rt-sht system in plants. *This shuld be dne as a grup in frnt f the whle class* Pur water int ne test tube and il int anther The tp f the liquid, where liquid meets the air, is called the meniscus. It lks different fr different liquids. -Examine the meniscus f the water and cmpare it t that f the il. What des it lk like? Hw are they different? The liquid with greater adhesive prperties will climb higher up n the side f the test tube Pur water int ne cup and il int anther Add fd dye clr f the kids chice t the cup full f water and f il s it is easier t see. Kids twist a piece f paper twel until in lks like a string. They then place ne end f the paper twel in the full cup f water and ne end in the empty glass. D the same fr the cup f il. Examine prgress at end f class. They shuld bserve that the water can travel up the paper twel and int the empty cup faster/mre than the il. Have yu seen this befre? Hw des this relate t hw plants get water frm the grund? Activity # 2 Drplet Materials Pipettes Cup f water Pennies Other liquids Wrksheet Nne This activity lks at the ability f water t frm sizable drplets due t chesin. When the drplet gets t large, the pressure inside it verwhelms the weaker frces f chesin acting n the surface, s the drplet bursts. Kids use pipettes t drp water nt pennies If there is extra time, they culd try t d the same with il r ethanl Befre they begin, ask hw many drps f water they think a penny can hld. Hw large can they get the water drplet befre it bursts? Which cin can hld the largest drplet? What happens when the cin is already wet? Are
there ther factrs that affect hw large the drplet can get? Wuld yu say the chesive frces are strng? Make sure they cmpare this t their daily bservatins abut water drplets n plants etc. Activity # 3 Surface Tensin Materials 1 glass filled with water Paperclip Paper twel Sap Wrksheet Nne This activity examines surface tensin by using this frce t flat a paperclip n the surface f water and seeing what kinds f things break surface tensin. Have kids put a paperclip in the glass f water and see that it just sinks t bttm. Why culdn t it flat? Why can little water bugs flat n tp f the water and nt this paperclip? Remve the paper clip and dry it Have kids tear ff a small piece f dry paper twel t place underneath the paperclip. Put bth twel and paperclip in the glass f water. The water will sak the paper twel, sinking it (yu may want t push the paper twel dwn with yur finger), leaving the dry paperclip t flat n the surface f the water. What was different this time? Did the paperclip weigh any less? Have kids put a drp f sap nt/near the paperclip and watch as the paperclip sinks. What happened here? What is imprtant t maintain surface tensin? Kids may then try this activity in the ther liquids. The paperclip did nt sink the secnd time because it did nt disturb the water s surface tensin; the paper twel did that jb fr it. The sap breaks the surface tensin and the paperclip sinks. Appendix f Inf fr Us Grwn-Ups Water has such high surface tensin, chesive, and adhesive prperties because f its ability t frm H-bnds. In bulk water, each water mlecule can frm 4 H- bnds. When adhering t ther surfaces, dispersive frces allw water t make weak bnds with ther materials; this causes capillary actin and the frmatin f a meniscus etc. Other kinds f liquids aren t typically able t make as many H- bnds; ethanl fr example, has a lwer surface tensin/chesive abilities Surface tensin and chesin are essentially different wrds fr the same prperty f water: its ability t make H-bnds. Adhesin has a different underlying mechanism
CONCLUSIONS Water likes t grab nt itself and thers, s it can hld weight, make drplet shapes, and travel up little tubes. These features are necessary fr sme f the things we see every day! Whenever a water drplet sticks t yur windw, r yu water a plant, think f all the different frces ging n in there!