Hy Density: Equalizing Matters (Equal Arm Balance)

Teacher Information Page Activity 3B Part 3

Activity Introduction:Students will make an equal arm balance and describe the difference between mass and weight. Students will also learn more about how Archimedes would have set-up his famous experiment to compare the golden crown to the known mass of gold.The activity takes only five minutes and students will use their equal arm balances in the nextpart of the activity.

Activity Background:Simply dropping a lump of gold in a container of water to determine the volume would nothave given Archimedes an accurate answer to his problem. How would he have gotten thelump out without spilling more water? What would he compare the displacement to? Heneeded more information.

Archimedes was the man who said“ΠΑ ΒΒΩ ΚΚΑΙ ΧΧΑΡΙΣΤΙΩΝΙ ΤΤΑΝ ΓΓΑΝΚΙΝΗΣΩ ΠΠΑΣΑΝ.”

Sorry, you might not know the ancientDoric language, of Syracuse.

Translation: “Give me a place to standand with a lever I will move the wholeworld.” Archimedes is attributed bymany as the person to come up withthe law of the lever.

It is believed that Archimedes com-bined what he learned in the bathtub(displacement of water and its relation-ship to density) and his knowledge oflevers. Before students can do the nextactivity they need to make an equalarm balance, which is a simple balancemade such that the distances from thepoint of support of the beam to eachpan at the end of the beam are equal,See Figure 1 Equal Arm Balance. Simple balances were used as early as 5000 B.C. More modern balances were devised in the 18th century, by the Scottish chemist Joseph Black. He used a lightweight, rigid beam supported on a thin-edged fulcrum. The accuracyachieved by this device was impressive.

These instruments operate in a way similar to that of a seesaw. A sample is placed on one end of the balance and then adding known weight to the other end until the beam balances.

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 1

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LESSON 3 ACTIVITY 3B PART 3

Figure 1 – Equal Arm Balance

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 2

Mass is the amount of material of which an object is made and is measured by using a balance. The balance allows us to compare an unknown amount of matter to a known amount of matter. When the beam is completely horizontal, the mass of the objects on both sides is equal. Thus we can determine the mass of an object. Weight is the pull of gravity on the mass of an object and is measured on a scale.

Activity Materials per group:� 3 large paperclips� 1 ruler with binder holes� Weight set or objects such as washers of known mass� 1 copy of Student Data Page (per student)� 1 copy of Student Information Page (from class set)

Students will make an equal arm balance similar to that shown in Figure 1 Equal Arm Balance.

Activity Management Suggestions:

Modifications:Time management may be the issue. This activity is designed to be completed in about 5 minutes, so be sure students understand all directions before starting to assemble the balances.

Extensions:Students can research the type of balance(s) used by Archimedes.Use a commercial double-pan balance to determine the accuracy of their balance.

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LESSON 3 ACTIVITY 3B PART 3

Hy Density: Equalizing Matters (Equal Arm Balance)

Student Information Page Activity 3B Part 3

Activity Introduction:It is believed that Archimedes would have used an equal arm balance to determine if there was a difference between crown and lump of gold. In this activity you will make an equal arm balance to use in your next experiment.

Activity Background:Simply dropping a lump of gold in a container of water to determine the volume would nothave given Archimedes an accurate answer to his problem. How would he have gotten thelump out without spilling more water? What would he compare the displacement to? Heneeded more information.

Archimedes was the man who said“ΠΑ ΒΒΩ ΚΚΑΙ ΧΧΑΡΙΣΤΙΩΝΙ ΤΤΑΝ ΓΓΑΝΚΙΝΗΣΩ ΠΠΑΣΑΝ.”

Sorry, you might not know the ancientDoric language, of Syracuse.

Translation: “Give me a place to standand with a lever I will move the wholeworld.” Archimedes is attributed bymany as the person to come up withthe law of the lever.

It is believed that Archimedes com-bined what he learned in the bathtub(displacement of water and its relation-ship to density) and his knowledge oflevers. Before students can do the nextactivity they need to make an equalarm balance, which is a simple balancemade such that the distances from the point of support of the beam to each pan at the endof the beam are equal, See Figure 1 Equal Arm Balance. Simple balances were used as early as5000 B.C. More modern balances were devised in the 18th century, by the Scottish chemistJoseph Black. He used a lightweight, rigid beam supported on a thin-edged fulcrum. Theaccuracy achieved by this device was impressive.

These instruments operate in a way similar to that of a seesaw. A sample is placed on one end of the balance and then adding known weight to the other end until the beam balances.

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 3

Corp

ulos

ity

LESSON 3 ACTIVITY 3B PART 3

Figure 1 – Equal Arm Balance

Mass is the amount of material of which an object is made and is measured by using a balance. The balance allows us to compare an unknown amount ofmatter to aknown amount of matter. When the beam is completely horizontal, the mass of the objects on both sides is equal. Thus we can determine the mass of anobject. Weight is the pull of gravity on the mass of an object and is measured on a scale.

Activity Materials per group:� 3 large paperclips� 1 ruler with binder holes� Weight set or objects such as washers of known mass� 1 copy of Student Data Page (per student)� 1 copy of Student Information Page (from class set)

Activity Instructions:

� 1. Gather the materials for your group.

� 2. Open the paper clips in such a way that you form a shape as shown in Figure 2 Open the Paperclips. You’ll notice that when the paper clip now has a “flat top” and a “hook” on the bottom portion.

� 3. You will notice that your ruler has holes in it. Take one of the open paper clips and slip in through one of the holes at an end on the ruler. The flat portion of the paper clip rests on the ruler.

� 4. Repeat this procedure with another paper clip; only slip it in the hole in the middle of the ruler. Again, the top flat portion of the paper clip rests on the ruler.

� 5. Repeat this procedure with the third paper clip; only slip it in the farthest hole at the other end of the ruler. The top flat portion of the paper clip should rest on the ruler.

2007 PROTOTYPE Positively Aging®/M.O.R.E.2007©The University of Texas Health Science Center at San Antonio 4

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LESSON 3 ACTIVITY 3B PART 3

Figure 2 – Open the Paperclips

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� 6. Hold the ruler up by the middle paper clip. You have made an equal arm balance! The ruler should be close to level. If it isn’t you need to make sure the paper clips on either end are in the correct holes. See Figure 3 Equal Arm Balance.

� 7. For practice in using the equal arm balance you just made, use the weight set or washers to determine the mass of two objects on your desk.

� 8. Save your Equal Arm Balance for the next section of the activity.

LESSON 3 ACTIVITY 3B PART 3

Figure 3 Equal Arm Balance

Paper Clips