## Measuring and Comparing Length, Weight, and Capacity: When Students Ask

• Why is knowing how to measure important?
Show children a recipe with the quantities removed. Ask them if they would be able to make the recipe as it is presented. Then discuss how people use measurement every day. People use it to measure how much fabric is needed to make clothing, to see how tall a building is, to measure how much water it takes to fill a pool, or to find out how much milk is in a container. Remind children that when they go for a checkup, the doctor measures their weight and height to make sure they are growing normally. Have children ask family members to give examples of when they use measurement. Ask volunteers to share the examples.

Discuss how having standard units of measure helps us to compare sizes and quantities. Have children think about how different their measurements were when they used different units to measure the same item. Explain to them that having a system of measurement with standard units like inches, kilograms, cups, and liters helps people communicate measurement more exactly than when they use nonstandard units. Ask children to describe what could happen in the following scenario: A family wants to buy a rug for their hallway. The mother measures the hallway with her own feet. When they get to the store, she tells the clerk how many feet of rug they need. The clerk then measures the rug with his or her own feet. Have volunteers suggest what could happen and then to justify their thinking.

• How can the same object have different measurements?
Have children use their hands to measure the length of a desk or table. Ask a volunteer to record his or her measurement. Then ask another child to compare his or her result. If the results differ, discuss why the results are different, pointing out that the hands are different sizes. Help children understand that the size of the measuring unit will affect the measurement. Explain that long ago, people used to measure using their own hands and feet, until they agreed on standard units.

Finally, have children measure a book in inches and compare the measurements. Discuss how using inches to measure is useful because an inch is always the same length, whereas human hands and feet can be different sizes.

• Is the biggest object always the heaviest?
Help children understand that larger objects do not necessarily weigh more than smaller objects. Provide an assortment of objects, including some large but light objects, such as an inflated balloon and a large empty cardboard box and some smaller, heavier objects. Ask a volunteer to choose two objects and to decide which is bigger and which is smaller. Record the answers. Then ask the child to hold each object and decide which is heavier. Emphasize the results, by stating them aloud, such as The balloon is bigger, but it is lighter. Point out instances in which the bigger object is lighter.
• Why don't the tallest containers always hold the most?
First show children a tall thin container, and then show them a short wide container with a greater capacity. Ask them to estimate which container can hold more. Have them test the capacities with sand or water. Help them to understand that taller containers don't necessarily hold more than shorter containers. Explain that a container may be tall, but if it is thin, it may not be able to hold as much as a shorter, wider container. Place a drinking straw next to a mug. Ask which is taller. Then ask which can hold more water. Since children have experience with straws, they should know how little liquid a straw can hold compared to a mug.
• How can I remember how many cups are in a pint and pints are in a quart?
Remind the children that the names of the containers come in alphabetical order from least to greatest amount held:cup,pint, andquart. This trick can help them remember the order. Point out that 2 cups equal 1 pint and 2 pints equal a quart.
• How much is a liter?
Pour water from a 1-liter bottle into a quart container to show that a quart is a little less than a liter. Explain that cups, pints, and quarts are from one system of measurement—the customary system—and that pints are from another system of measurement—the metric system. Discuss the fact that customary units are used in the United States and metric units are used in many other parts of the world.