science tools using a balance scale - wikispaces · pdf filescales often measure weight in...

Science toolS

Using a Balance Scale

© Learning A–Z All rights reserved. www.sciencea-z.com1

Purpose To accurately use a balance scale to compare the weights of objects.

Process Skills Predict, observe, measure, collect data, interpret data, communicate, identify and control variables, draw conclusions

BackgroundThe amount of material that a thing is made of is called its mass. When we measure how heavy a mass is, we call that number its weight. On Earth, the weight of an object is the same as its mass.* We can use a scale to measure weight. Scales often measure weight in grams, kilograms, ounces, or pounds. Scientists usually use grams and kilograms to measure weight. One gram (g) is about equal to the weight of two small paper clips. One liter (1,000 g) of water weighs one kilogram (kg).

A balance scale is a tool that can be used to compare the weights of two objects. A balance scale is like a seesaw. When one object is heavier than the other, the scale is unbalanced, and the heavier object drops below the level of the lighter object. When the scale is balanced, we know that the objects on both sides weigh the same. Or we can weigh an object by placing it on one side of the scale and adding standard units of measure (such as gram or kilogram weights) to the other side until the scale is balanced.

Time – Preparation: 10 minutes; Part 1: 10 minutes; Part 2: 30 minutes

Grouping – Small groups

Materials(per group) q Data Sheets 1 and 2q balance scaleq 5 toothpicksq set of 10 lightweight classroom objects

(1 unsharpened pencil and 9 other items, such as student scissors, glue stick, watercolor paintbrush, marker, or crayon)

q box or bag of small paper clips

In almost every task in life, people use tools. Doctors cut with scalpels, construction workers dig with shovels, and artists paint with brushes. Science is no different. Many tools can help you measure the results of your observations and experiments. These tools can make your job easier and make your results more precise.

*On other planets, an object that has the same mass as it did on Earth might weigh more or less, depending on the force of gravity there.

Figure A

beambase

fulcrum

pan

pointer

2

EXPLORATION Science Tools—Using a Balance Scale

© Learning A–Z All rights reserved. www.sciencea-z.com

ProcedurePreparation

1. Get a balance scale and five toothpicks from your teacher. Make sure to place your balance scale on a level surface.

2. In your group, take turns pointing to each of the balance scale’s parts (See Figure A on page 1). Locate the fulcrum, base, beam, pans, pointer, and adjustment dial (if there is one). If you need help, look at Figure A and compare it to your scale.

3. In order to get accurate measurements of weight, check to make sure that your scale is “zeroed out.” This means the line or lines in the middle of the scale must be pointing to the exact middle before you weigh anything. Your scale may already be perfectly balanced. But if your scale does need to be adjusted, first see whether it has a dial that you can turn to zero it out. If there is no dial, try placing a toothpick onto the higher side of your scale to make it even with the other side. If the toothpick is too heavy, break it in half and try again until the scale is zeroed out. You may need to add more toothpicks or other items until the scale is level.

4. If you have had to adjust your scale by adding toothpicks, make sure to leave the toothpicks on the scale while you do Part 1 and Part 2.

Part 1: Comparing Weights

1. Gather a set of ten lightweight classroom objects, including an unsharpened pencil. Write the names of all the objects in the first column of Data Sheet 1.

2. Take turns holding each object in your hand. As a group, discuss which objects feel heaviest and which objects feel lightest.

3. On Data Sheet 1, record predictions. Which objects will weigh more than the unsharpened pencil? Which objects will weigh less than the pencil? Will any objects weigh the same as the pencil?

4. Now use your scale to compare the weights of the other objects to the weight of the unsharpened pencil. Start by placing the unsharpened pencil on one side of your zeroed-out scale. One at a time, place each of the other objects on the opposite side of the scale. Compare the weights of the other objects to the weight of the pencil (See Figure B).

Figure B



3. Place the unsharpened pencil on one side of the scale. Add pairs of paper clips to the other side of the scale until the scale is balanced (see Figure C). You will know that your scale is balanced when the lines match the zeroed-out position. Add or remove a single paper clip if necessary to add or subtract about half a gram.

5. Which objects weighed more than the pencil (making that side of the scale drop lower than the side with the pencil)? Which objects weighed less than the pencil (making the pencil side of the scale drop lower)? Which objects weighed the same as the pencil (making the two sides of the scale even, in the zeroed-out position)? On each row of Data Sheet 1, place a check mark (3) in the correct box to compare each object’s weight with the weight of the pencil.

Part 2: Measuring the Weights of Objects

1. Get a box or bag of small paper clips from your teacher. Connect some of the paper clips in pairs.

2. Use Data Sheet 2 to make a prediction about how much the pencil will actually weigh. Predict the number of paper clips it will take to balance the scale and how many grams the pencil will actually weigh.

TIP: Each set of 2 paper clips weighs about 1 gram (1 g). A single paper clip weighs about one-half of a gram (0.5 g). For example, if you think that your pencil will weigh the same as 15 paper clips, the predicted weight would be about 7.5 grams.

Figure C

4. Use Data Sheet 2 to record the number of paper clips it actually took to balance the scale. Also record the actual weight of the pencil (in grams).

5. Repeat steps 2, 3 and 4 for each of the remaining lightweight objects. First, record a prediction of its weight, both in paper clips and in grams. Then place each object on one side of your scale and use paper clips to find its actual weight. Record the results on Data Sheet 2.

= 1 gram

4© Learning A–Z All rights reserved. www.sciencea-z.com

Part 1: Comparing WeightsPredict: Which objects will weigh more than the pencil? Which objects will weigh less than the pencil? Which objects will weigh the same as the pencil?

Collect Data

ObjectWeighs more than the unsharpened

pencil

Weighs less thanthe unsharpened

pencil

Weighs the same asthe unsharpened

pencil

Unsharpened pencil 3

EXPLORATION Science Tools—Using a Balance Scale Data Sheet 1

Name________________________________________ Date_____________

4

5© Learning A–Z All rights reserved. www.sciencea-z.com

Part 2: Measuring the Weights of ObjectsCollect Data

ObjectPrediction:Number of paper clips

Prediction: Weight in grams (g)

(predicted number of paper clips ÷ 2)

Actual:Number of paper clips

Actual:Weight in grams (g)

(actual number of paper clips ÷ 2)

Unsharpened pencil


Name________________________________________ Date_____________

5

6

EXPLORATION Science Tools—Using a Balance Scale Questions

Name________________________________________ Date_____________


Analyze Data1. Describe exactly what you had to do to zero out your scale.

2. Did any objects weigh an equal amount? If yes, which objects? If no, which objects were closest to equal?

3. Which object weighed the most? How many grams did it weigh? Which object weighed the least? How many grams did it weigh?

4. Which object’s predicted weight was the closest to its actual weight? Why do you think your prediction was the closest for this object?

5. Suppose one of your objects took 11 paper clips to balance. What would the weight of this object be?

6. Look at Data Sheet 2 to find out how much your unsharpened pencil actually weighed (in grams). How much would 3, 10, and 47 unsharpened pencils weigh?

1 pencil = ______ grams 3 pencils = ______ grams 10 pencils = ______ grams 47 pencils = ______ grams

Draw Conclusions1. Why is it useful to know how to use a scale? List three reasons you might use

scales outside of school.

2. In your own words, explain how a balance scale works.

3. If your teacher asked you to build your own balance scale using materials from the classroom, how would you build it? (Use the back of the paper.)

Most: Weight: g Least: Weight: g


Teaching TipsThis process activity will help students understand how a balance scale works. Students will learn how to zero out a scale and predict weight in grams. Students will also gain experience as they explore the weights of common classroom objects and use the data to calculate and compare weights. As they relate weight to common objects, students may come to appreciate how a scale helps people in a variety of settings. Practicing using a scale and comparing the weights of objects will also help students estimate the weights of solids in many applications.

¢ Beforestudentscompareandmeasuretheweightsofobjects,youmaywanttoconductyourownmeasurementswiththeitemstheywillbeweighingsoyouwillbeabletojudgewhetherstudents’resultsarereasonable.

¢ ProvidetimeforstudentstozeroouttheirscalesbeforebeginningPart1.¢ Reinforcevocabulary(balance scale, base, fulcrum, beam, pans, pointer, zero out,

adjustment dial)whilemodelinghowtozerooutthescale.ItmaybehelpfultorefertothelabeleddiagraminFigureA,butexplaintostudentsthatscalescomeinmanyvarieties.ThebalancescaletheyusemaynotlookthesameastheoneinFigureA.

¢ Ifanythinginthestudentsetofobjectstoweighismuchheavierthantheunsharpenedpencil,studentswillneedtoomanypaperclipstoassesstheweight.Instead,encouragethemtouseunsharpenedpencilsasweights,eachonerepresentingacertainnumberofpaperclips(seePart1,step4oftheProceduresection).Individualpaperclipsmaythenbeaddedtothepanholdingthepencilsuntilthescaleisbalanced.Instructstudentstorecordthetotalweightinpaperclips.

materials ¢ Manydistrictshaveascienceresourcecentertocontactifbalancescalesarenotavailableattheschool.Simplebalancescalescanalsobeconstructedusingdirectionsavailableonline(searchfor“homemadebalancescale”).Otherwise,scalescanbepurchasedatlocaloronlineteachersupplystores.

¢ Preparesetsoftenlightweightclassroomobjectsforeachgroupbeforehand.Makesureeachsetisthesamesothatgroupscancomparedata.Eachsetmustincludeoneunsharpenedpencilandnineotheritems,suchasstudentscissors,agluestick,awatercolorpaintbrush,acaperaser,amarker,acrayon,acoloredpencil,orapieceofpaper.

¢ BesurestudentsusesmallpaperclipsinPart2.¢ Alargebaggiemaybeusedtoholdthesetofobjectsforeachgroup.

However,studentsshouldweigheachobjectwithoutthiscontainer.¢ Additionalunsharpenedpencilsshouldbeavailabletostudentsforuse

inPart2,step5iftheyhavechosenheavierobjects.

set-up and procedures

science tools

Using a Balance Scale



¢ Variation/Inquiry Science:Afterstudentshavecomparedthedryweightofclassroomitems,allowthemtousetheirbalancescaletocompareliquidsusingsmallplasticcondimentcontainers.Examplesincludewater,milk,juice,syrup,oroil.Forexample,does100mLofwaterweighmoreorlessthan100mLofmilk?(Notethatliquidismeasuredbyvolume,notweight.Milliliters[metric]andfluidounces[standard]areused,sopaperclipsarenotvalidasmeasurementtools.)

¢ Variation/Math:Havestudentsdeterminetheweightoflargepaperclipscomparedtotheweightofsmallpaperclips.Mostsmallpaperclipsweigh.5grams,andmostlargepaperclipsweigh1.5grams.Encouragestudentstodrawbalancedequationsthatshowtherelationshipbetweensmallandlargepaperclips.Thenallowstudentstimetodeterminetheweightsoftheirobjectsusingbothlargeandsmallpaperclips.

¢ Community Service/Field Trip:Foodbanksweighdonations.Takeatriptoalocalfoodbank,equippedwithitemstodonate,andtalktothefoodmanagerabouthowweightisusedthere.Ifpossible,askwhetherstudentsmayweighsomeofthefooddonations.Recyclingcentersmayalsoprovideopportunitiesforstudentstoparticipateinweighingforanauthenticpurpose.

¢ Inquiry Science:Allowstudentstoexploredifferenttypesofsame-sizedpaper.Howmanypiecesofcopypaperdoesittaketobalanceoutonesheetofcardstock?Cardboard?Papertowels?Doeslinedpaperweighthesameascopypaper?Doesallcopypaperweighthesameamount?Doesfoldedpaperweighthesameasflatpaper?

¢ Writing:Havestudentswriteapoemorashortstorythatcomparestheweightofanaveragemouse(20grams)tootherobjects.Forextensivewritinginstruction,visit .

¢ ELL/ESL:Createawordwall.Includecontentvocabularysuchasbalance scale, zero out, fulcrum, beam, pans, pointer, adjustment dial,andgram.Alsoincludevocabularyrelevanttothelesson,suchasunsharpened pencil and paper clip.Formorevocabularyresources,visit .

¢ Technology:HavestudentscreateaPhotoStoryorPowerPointpresentationaboutthebalancescale.Studentsmaysharetheresultsoftheirexploration,thehistoryofthebalancescale,andpicturesofvariousbalancescales.

¢ Home Connection:Challengestudentstocreatetheirownbalancescaleathomeusingeverydayobjectsonly.Askstudentstobringtheirhomemadescaletoclasstobeusedinfurtherpractice.

extensions andvariations



70%

answer key

Results will vary, depending on the set of objects each group is given. For each object, students should use their prior knowledge to make a reasonable prediction. The table below reflects possible data, based on common lightweight classroom objects. Note that the results recorded below may vary from your own school supplies; conduct your own measurements before assessing student data sheets.


Part 1: Comparing WeightsPredict: Which objects will weigh more than the pencil? Student predictions will vary.Which objects will weigh less than the pencil? Student predictions will vary.Which objects will weigh the same as the pencil? Student predictions will vary.

Collect Data

ObjectWeighs more than the unsharpened

pencil

Weighs less thanthe unsharpened

pencil

Weighs the same asthe unsharpened

pencil

Unsharpened pencil 3

Student scissors 3Glue stick 3Watercolor paintbrush 3Cap eraser 3

Marker 3Crayon 3

Colored pencil 3Copy paper, 1 sheet 3Sharpened pencil 3


Name________________________________________ Date_____________

4



70%

answer key

Results will vary, depending on the set of lightweight objects each group is given. The table below reflects possible data, based on common lightweight classroom objects. If the sets that you have assembled for your classroom vary from the objects below, conduct your own measurements before assessing student data sheets.


Part 2: Measuring the Weights of ObjectsCollect Data

ObjectPrediction:Number of paper clips

Prediction: Weight in grams (g)

(predicted number of paper clips ÷ 2)

Actual:Number of paper clips

Actual:Weight in grams (g)

(actual number of paper clips ÷ 2)

Unsharpened pencil

For each object,

students should use their prior knowledge to make a reasonable prediction.

Each predicted

weight in this category should be calculated

on the basis of the

predictions made in the first column.

For example, if a student

predicts that a cap eraser

will weigh the same as five paper clips, the predicted weight will be

half of that amount

(5 ÷ 2 = 2.5 g).

11 5.5 g

Student scissors 54 27 g

Glue stick 30 15 g

Watercolor paintbrush 4 2 g

Cap eraser 6 3 g

Marker 24 12 g

Crayon 11 5.5 g

Colored pencil 12 6 g

Copy paper, 1 sheet 2 1 g

Sharpened pencil 10 5 g


Name________________________________________ Date_____________

5



answer key and explanaTionsAnalyze Data1. Describeexactlywhatyouhadtodotozerooutyourscale.

Answers will vary, depending on the type of balance scale available in your classroom and students’ methods for zeroing out their scales. Answers should include an explanation of the process.

2. Didanyobjectsweighanequalamount?Ifyes,whichobjects?Ifno,whichobjectswereclosesttoequal?

Because each set of lightweight classroom objects will vary, conduct your own measurements before assessing students’ answers to this question.

3. Whichobjectweighedthemost?Howmanygramsdiditweigh?Whichobjectweighedtheleast?Howmanygramsdiditweigh?

Because each set of lightweight classroom objects will vary, conduct your own measurements before assessing students’ answers to this question.

4. Whichobject’spredicted weightwastheclosesttoitsactual weight?Whydoyouthinkyourpredictionwastheclosestforthisobject?

Answers will vary and should include an explanation.

5. Supposeoneofyourobjectstook11paperclipstobalance.Whatwouldtheweightofthisobjectbe?

11 ÷ 2 = 5.5 grams

6. LookatDataSheet2tofindouthowmuchyourunsharpenedpencilactuallyweighed(ingrams).Howmuchwould3,10,and47unsharpenedpencilsweigh?

Because each set of lightweight classrooms objects will vary, conduct your own measurement of the unsharpened pencil before assessing students’ answers to this question. The answers provided below are based on an unsharpened pencil that balances with 11 paper clips. Since 11 paper clips weigh 5.5 grams, students should calculate their answer by multiplying the number of pencils by 5.5. Thus, the results would be as follows:

1pencil=5.5grams 3pencils=16.5grams10pencils=55grams 47pencils=258.5grams

Most: Weight:g Least: Weight:g



answer key and explanaTions

Draw Conclusions

1. Whyisitusefultoknowhowtouseascale?Listthreereasonsyoumightusescalesoutsideofschool.

Answers will vary. It is useful to know how to use a scale for many reasons. Doctors keep track of children’s weight to make sure that they are growing. People weigh food at the grocery store or deli. Airlines use scales to make sure that a plane doesn’t carry too much baggage.

2. Inyourownwords,explainhowabalancescaleworks.

Answers will vary. The weights of objects can be compared using a balance scale. Assuming that the pans are an equal distance from the fulcrum, an object that weighs more will be on the lower side of the scale. If an object weighs less, it will be on the higher side of the scale. If objects weigh the same amount, the scale will be parallel to the ground or tabletop.

3. Ifyourteacheraskedyoutobuildyourownbalancescaleusingmaterialsfromtheclassroom,howwouldyoubuildit?(Usethebackofthepaper.)

Answers will vary but should indicate a basic knowledge of a balance scale’s parts, especially the fulcrum and beam. Students might include a sketch or diagram.

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