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How is the Surface Tension of Water Affected By Soap?

.lntroduction: Surface tension of water is a force exerted by the surface of water on the particles below.

It results from the attraction of water molecules to other water molecules. The force of surface tension

tends to pull drops of water into spherical shapes. When drops of falling water are photographed with a

high-speed camera, their shape is visible. Surface tension refers to water's ability to "stick to itself".

Surface tension can be measured and observed by dropping water (drop by drop) onto a penny. The

number of water drops that can fit on a penny will surprise you.

1. lnitial Observation: Observe surface tension by seeing how many drops ofwater can fit on a penny.

Number of Drops I I

Question: How does soap affect the wa.ter's surface tension?

2. Develop a hypothesis that answers the experimental question' Write your

hypothesis below. -.1. + iliprii "",{:i.lil "ict";f"r"l'' * i'"'e -:r t f irr"t*enti{{""' ,rr.:1,\it ht ,.i,f"r,rr".1r itsi rrn+e f L^Jt{[ S-lCl,,., f,,r',

i l.f t:,6iri'r.,.}3. Test your hypo[hesis by comparing the number of drops of tap water thatcan fit on a penny to the number of drops of soapy water that can fit on a penny. Because water drops

may vary depending on how wellyou dr.op the water, it is best to run many trials and take an average.

Record your data in the table below

Trial 1'Trial 2 Trial 3,trial+ ;Trial5 . Average

Tap Water

Soapy Water

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3. Create a graph that best represerits all of your data._23

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4. Define surface tension. 1 L 5 Ll 5 A{cragg T nG l

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5. Was your hypothesis supported or rejected? Support with specific data.

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6 Suggest a reason for your observations and data (Why did it happen?).

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,*7. Why were many trials taken bnd averaged?

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8. What is an experimental constant? Why is importqnt to keep aspects of an experiment constant?

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9. What is a control? ln this experiment, what is your control gr.oup?

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10. What is an indUpendent variable? ldentify the independent variable in the experiment.

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11. What is a iJependent variableT ldentify the dependent variable inthe experimefrt.

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12. Name the 5 unique properties of water. liennt . I1 f{nrfSiCn

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4. Uat ua\ilt SOt vefits. +frhrsim13. People usually think of water as being wet. lf water alone is used to wash clothing, however, it-docsn'tpenetralethclabriereryw-fl.'BasEd*on what-yon observed in-the1ab, how doesthe addition ofdetergent make water "wettdr", that is, more capable of penetrating the pores of the fabric?

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