fat: who says? measuring obesity by bioelectrical ... · the human body has many electrolytes,...

Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio

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LESSON 3 ACTIVITY 3C, PART C

Fat: Who Says? Measuring Obesity by Bioelectrical

Impedance Analysis

Circuitous Adventures-Conductors and InsulatorsStudent Information Page 3C Part C

Activity Introduction: So which materials can conduct electricity and which ones cannot? That’s what you will findout as you complete this activity.

Activity Background:An electrical conductor is a material that allows electrical current to flow freely. An electricalinsulator is a substance that does not allow electrical current to flow freely. A homogeneoussolution is composed of one or more substances dissolved in another substance; such thatthe original substances are no longer distinguishable. An example of a homogenous solutionwould be salt water because the salt breaks apart into ions when salt is placed in water. Aheterogeneous mixture consists of visibly different substances combined. An example wouldbe sugar water, because the sugar will eventually separate at the bottom of the glass as it“falls out” of solution. The human body is quite complex and made of many different materi-als; some of these are be conductors, while others are insulators; some are homogeneous andsome are heterogeneous.

Why are some materials conductors and others non-conductors? Metals allow the free movement of electrons and thus are able to carry an electrical current. What about non-metals that are conductors? We need to look at something called ions. Ions are electrically charged elements because they have either gained or lostelectrons. When compounds such as acids, bases, and salts are dissolved in water, ions areformed. Acids, bases, and salts are ionic compounds, which dissolve in water to produce bothpositive and negative ions called electrolytes. Non-ionic compounds do not break into ionswhen dissolved in water; sugar is an example.

The human body has many electrolytes, which are positively and negatively charged particles (ions) that form when salts dissolve and separate (dissociate) in water. Electrolytebalance is important to the normal functioning of cells, nerves, muscles, blood pressure, andglands. When electrolytes become unbalanced, as in excessive sweating, vomiting, diarrhea,or serious burns and wounds, they need to be replaced. With severe electrolyte loss, lifethreatening conditions can arise.


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Figure 1 Creating a Break in the Circuit

Testing the Materials Between the Break

Break in the Circuit

Cotton Ball

Battery

Bulb or BuzzerBreak in Circuit

Battery Bulb

Activity Materials: (per group or station)Dry Materials:• 1 Toothpick• 1 Rubber band• 1 Cotton ball• 1 Small piece paper towel• 3 metal wires, each made of different metal • Battery• Buzzer or bulb• 1 piece of lead (graphite) from the center of a pencil* Wet Materials:• 5 plastic cups labeled and 1/2 filled with distilled water, tap water, sugar water,

salt water, and butter

• 1 Copy Student Information Page• 1 Copy Student Data Page• Paper towels or baby wipes with which to clean up.

* Woodless Graphite sticks can be used instead of pencil leads(These can be found in the drawing sections at craft stores such as Hobby Lobby. They are approximately 6 mm thick and 15 cm long. A sharp knife can be used to scrape off a thin coating along the 15 cm length)

Activity Instructions:1. Gather your materials. Be sure your get five cups - You will need one for distilled

water, tap water, sugar water, salt water, and butter.

2. Set up the simple circuit as you have used in previous parts of this activity. Create a break between the switch and the buzzer, see Figure 1.

3. Before you actually test each of the materials, on your own paper, create adata table that has a column in which you predict whether that material will

conduct electricity and one to record if it actually did conduct electricity. There are 14 different materials to test.


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4. Using the dry materials first, place one item across the break so that each exposed wires from the circuit touch one end of the object. See Figure 1. Repeat this step for all other dry materials. Remember: If you hear the buzzer or see the bulb light up, then that material has completed the circuit and that material conducts electricity.

5. Saving the butter for last, test the liquid materials next. Put both ends of the broken circuit into the cup and submerge them in the liquid.

� Make sure the two exposed metal ends of the circuit are NOT touching each other in the liquids.

� Be sure to dry off the ends BEFORE placing them in the next cup you are testing.

6. Record all your results in the chart and indicate if the buzzer sounded.

7. Now mix the salt water with the sugar water. Create a new row on your chart (14th

item). Predict if this mixture will conduct electricity. Test your new mixture and recordthese results in your chart.

Processing Out:1. Make a T-chart and list all the conductors you found on one side of the chart and all

the non-conductors (insulators) on the other.

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Conductors Non-conductors


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2. Were your predictions correct? Which were not correct?________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. The salt water is a homogeneous solution. Define the word homogenous. ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. When mixed, sugar water and salt water forms a heterogeneous mixture. Define the word heterogeneous.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. How does the conductivity of this new heterogeneous mixture compare to the conductivity of each of the liquids separately?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

6. Using the background information included in this activity, explain why salt water conducts electricity and sugar water does not?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

7. Why do you think that the combination of salt and sugar waters conducted electricity?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

8. How does this relate to your body and electrical flow?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

fat: who says? measuring obesity by bioelectrical ... · the human body has many electrolytes,...

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