•      Students use their bodies to indicate the    relative weights of two different objects.

• Compare weights by feeling the difference between them
• Model a pan balance with the body

Prior Knowledge

• Identifying common objects

Materials

• A variety of objects of noticeably different weights that children can hold in their hands (a heavy book, a paperweight, a stapler, a boot, a scarf, a piece of paper, a toothbrush, paper clips); a large, lightweight object, sich as a piece of plastic foam; a small, heavy object, such as a paper weight
• A pan balance (If available)
• For each group of two or three students, three heavy items, three light items, and two items that weigh about the same
• A copy of the blackline masters "Body Balance" and "Possible or Not?" for each student (See Dottie for these)

Activity

Engage:   Show the students a pan balance if one is available. Identify the instrument, and tell the students that its purpose is to show which of two objects is heavier. Place a heavy book (or another heavy object) on one side and a paper clip (or another light object) on the other side of the balance. Have the students tell you how they can identify the heavier object by using the pan balance.     Hold your arms straight out and parallel with the floor, and tell you how they can identify the heavier object by using the pan balance.   Hold your arms straight out and parallel with the floor, and tell the students that you are going to pretend to be a pan balance: If the objects in your  hands weigh the same, your arms will stay parallel with the floor, and your hands will be even. If you hold a heavy object on one side, lean from the waist toward the sidfe holding the heavier object, and drop one arm as you raise the other. Dramatize a "body balance" by  holding the heavy book in one hand and the paper clip in the other. Bend toward the floor on the side holding the book to show that the book is heavier than the paper clip. Talk with the students about why  your body leaned over. (because the book weighs more than the paper clip).   Display two objects of noticeably different weights, such as a boot and a scarf. Tell the students that you will be holding the boot in one hand and the scarf in the other. Show them which hand will hold each object. Have them predict which way your body will lean. Then pick up the two objects and lean to show which is heavier.
(You should exaggerate the lean of your body to help clarify the concept.)   Ask questions like the following:

• Why did my body lean to the left (or right)?
• What would happen if I switched the scarf and the boot from one hand to the other?

   Explore:  Organize the students into groups of two or three, and distribute the objects. Encourage each student to pick up two objects of noticeably different weights, one in each hand, to see which feels heavier. Have the students use their bodies as balances to model the relative weights of the two objects. After the students have compared objects that differ considerably in weight, reduce the differences between the objects until the objects weigh about the same.    Initiate a discussion of what the students think makes an object heavy or light. Be prepared for misconceptions to arise. For example, some students assume that anything large is heavy and anything that is small is light. To help the students understand that this assumption is not always correct, let them feel a small, heavy object, such as a paperweight, and a largem lightweight object, such as a piece of plastic foam.    Give each student a copy of the blackline master "Body Balance" to complete individually. Explain that in numbers 1-4, the students should draw a line from each object to the hand they think is holding it. In number 5, the students should draw objects that will make the body balance correct. After all the students have finished the worksheet, talk with the class about what objects the students drew in the balance for number 5 and how they know that the objects weigh the same.

Extend:   Model a "preposterous" balance situation; that is, place an object in each hand and lean toward the lighter one. Talk about why this situation makes no semse. Give the students a copy of the blackline master "Possible or Not?" After completing the work individually, have a class discussion about their choices.

Using the body as a balance is more immediately meaningful than using a pan balance because the students can actually feel the weight pulling them farther down on one side than the other.

Navigating through Measurement NCTM

E-mail Dottie if you would like her to model this for your class