The Human Balance Scale

Expectations:

E2.2 compare several everyday objects and order them according to length, area, mass, and capacity

Key Concepts

• Objects can be compared and ordered according to whether they have more or less of an attribute. Comparing the same objects by different attributes may produce different ordering.

• There are specific words and phrases that help describe and compare attributes:

  1. more, less, smaller, and bigger often only describe general comparisons unless a specific attribute is included (bigger area; smaller capacity);

  2. adding the suffix “-er” or “-est” typically creates a comparative term (e.g., heavier, lighter, heaviest, lightest).

• Objects can be directly compared by matching, covering, or filling one object with the other to determine which has more length, mass, area, or capacity.

• When a direct comparison cannot be easily made, a third object can serve as a “go-between” tool to make an indirect comparison. For example, a third container can be used to determine which of two containers holds more water. Indirect comparisons require using the transitivity principle and the conservation principle.

• Show students a balance scale and demonstrate how it can be used to compare the weights of two small objects.

• Call for several students to take turns being a “human balance scale” by each holding objects such as a small box of paper clips on one outstretched palm and a box of chalk on the other outstretched palm. Ask them to close their eyes and then to think and decide which object feels heavier. Write their answers on the board.

• Students are often surprised to find that size and weight are not always directly correlated. Objects that are the samw size may have different weights, and a large object can weigh less than a small one.

• Ask children to predict how the real balance scale would look if the box of paper clips is heavier and it would look if the box of chalk is heavier.

• Put the boxes on the balance scale to find the actual outcome.

How can you use a block of 50 snap cubes to weigh classroom objects?

• With a partner, count out 50 snap cubes.

• Snap the cubes together to form a block

• Find a small object in the classroom.

• Compare the weight of the object to the weight of the snap cube block. Here’s how:

  • Hold the object in the palm of one hand. Hand the snap cube block in the palm of the other hand

  • Close your eyes. Decide if the object weighs more than, less than, or about the same as the snap cube block

  • Make sure both you and your partner compare the weights. Then come to an agreement about how the weights compare.

• Find objects that fit into all of these categories:

  • Weights more than the snap cube blocks

  • Weighs less than the snap cube block

  • Weighs about the same as the snap cube block

Place the three loops of string (or hula hoops) on the floor in front of the room and label them “weighs more, weighs less, weighs about the same”. Have children place their objects into the appropriate circles. Then use the balance scale and a block of 50 snap cubes to weight each object. After weighing, put each object back into the circle with the label that correctly compares its weight to the block of snap cubes.

***You may not have time to weigh each object. This could be put out as a centre or a follow up activity.***

Use prompts such as these to promote class discussion:

• For which circle was it easiest to find objects? Why?

• For which circle was it hardest to find objects? Why?

• (Take one object from a circle) This object came from the circle labeled _____. If it was placed correctly, how would the balance scale look with the block of snap cubes on one side and this object on the other side?

• (Place an object and the snap cube block on the balance scale). Since the balance scale looks like this, how does the weight of the object compare to the weight of the snap cubes?

• (Hold up two objects that were just weighed). Now that you have seen the weight of each of these two objects compare to the weight of the snap cube block, how do you think their weights would compare with each other?

• Ask a student to pick up an object that they know weighs more than the snap cube block. HAve them draw a picture of what the balance scale would look like with these two objects on it. Then, have them use words to describe what they drew.

• Have students make a block of 80 snap cubes. Ask how they will have to rearrange the objects already in the labeled circles if they are now comparing the objects’ weights to the 80 snap cube block.

• Ask children to predict how many snap cubes it will take to balance a pencil. Have them use the balance scale to check their predictions and compare their results with others.

• Challenge students to suggest which combination of objects from the circle labeled “weighs less than” might exactly equal the weight of 50 snap cubes. Have them make some predictions and then test them on the balance scale.

SEL Student Self Reflection and Teacher Rubric

Extension Activities:

• Have students use a balance scale to compare pairs of cuisenaire rods of varying lengths (or sets of unifix cubes) to model number sentences for addition, such as 7+4=11. To model this particular number sentence, ask students to place a rod that is 7 units long in one pan and then add a 4 unit long rod to that pan. Ask them to find which rod is needed to balance the pan. The 11 unit long rod would balance the 7 and 4 unit rods in the other pan.

• Have students use a pan balance to compare four objects of noticeably different weights. They should start by placing any two objects in the balance, one on either side. They will leave the heavier object in and place a new object in the opposite pan. Students should keep repeating this procedure to check all four objects until they determine the heaviest one in the collection. They can then find the lightest object in the set of three remaining objects by repeating the procedure, starting with one of the three objects.

• K-2 SuperSource - Base Ten Blocks: “Balance of Values” pg. 18