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An object could be on Earth. Or it could be on the moon. The object’s mass would not change. But its weight would change. This is because weight depends on gravity. Gravity is a force that pulls objects toward one another. Weight is the force of gravity affecting an object. Earth’s strong gravity pulls people and objects toward its center. The force of gravity is smaller on the moon. People and objects would weigh less there.

Pounds are a unit of weight. Kilograms are a unit of mass. But people often use both to talk about weight. On Earth, the difference between a person’s weight and mass is very small. For this reason, people often ignore the difference. They treat weight and mass as if they are the same thing. For example, this scale shows both pounds and kilograms.

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Making Connections


Have you ever had your weight measured? What kind of scale did you use?


Weight and gravity are related. Have you read other books about gravity? What did you learn?


Why might it be useful to know the weight of something?

Teacher Resources

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