Mass vs Weight

Mass vs Weight

Middle School

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Learning Objectives

Key Vocabulary

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Mass

A measure of the amount of matter or stuff in an object; it is always constant.

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Weight

The measure of the force of gravity on an object, which can change with location.

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Newton (N)

The standard (SI) unit of measurement for force and weight, a fundamental concept.

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Scalar Quantity

A quantity that has only magnitude, or size, but no direction, such as mass.

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Vector Quantity

A quantity, like weight, that has both a magnitude and a specific direction.

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What Are Mass and Weight?

• Mass is the amount of matter or "stuff" that is in an object.

• ​An object's mass is constant and its standard unit is the kilogram (kg).

• Weight is the measurement of the force of gravity pulling on an object.

• An object's weight depends on its mass and is measured in Newtons (N).

Multiple Choice

Which statement accurately describes the fundamental difference between mass and weight?

• Mass and weight are two different words for the exact same property of an object.

• Mass measures the amount of matter in an object, while weight is the force of gravity acting on it.

• Mass is the force of gravity on an object, while weight is the amount of matter it contains.

• Mass is measured in Newtons (N), and weight is measured in kilograms (kg).

Key Differences: Mass vs. Weight

• Mass is the amount of matter in an object and is always constant.

• Weight is the force of gravity on an object, so it can change.

• An object's mass is the same everywhere, but its weight can change.

Multiple Choice

An astronaut travels from Earth to the Moon, where the gravity is much weaker. How do her mass and weight change?

• Both her mass and her weight decrease.

• Her mass decreases, and her weight stays the same.

• Both her mass and her weight stay the same.

• Her weight decreases, but her mass stays the same.

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Calculating Weight on Earth

Multiple Choice

Using the formula $$W=mg$$ , what is the weight in Newtons (N) of a bicycle with a mass of 15 kg on Earth? (Use $$g=9.8m/s^2$$ )

• 1.53 N

• 147 N

• 15 N

• 24.8 N

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Weight on Other Worlds

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Multiple Choice

An exploratory rover has a mass of 150 kg on Earth. What would its weight be on Mars, where the gravity is 0.39G?

• 384.6 N

• 58.5 N

• 150 N

• 91.5 N

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Common Misconceptions About Mass and Weight

Misconception	Correction
Mass and weight are the same.	Mass is matter in an object. Weight is the force of gravity on it.
Objects in space have no mass, so they are weightless.	Objects in space have mass. They seem weightless because of very low gravity.
Kilograms (kg) and pounds (lb) measure the same thing.	The kilogram (kg) measures mass. The pound (lb) and Newton (N) measure weight.

Multiple Choice

Why does a person's weight differ on Mars compared to Earth, even though their mass remains identical?

• The force of gravity is different on Mars than it is on Earth.

• The different atmosphere on Mars affects the measurement on a scale.

• Mass and weight are the same, so both would change on Mars.

• The person loses some of their matter while traveling through space.

Multiple Choice

If a moon rock weighs only one-sixth on the Moon what it does on Earth, what does this imply about the Moon's gravitational pull?

• The Moon's gravitational pull is one-sixth as strong as Earth's.

• The rock's mass changes to one-sixth of its original amount on the Moon.

• The Moon's gravitational pull is six times stronger than Earth's.

• The Moon has no atmosphere, which makes objects feel lighter.

Multiple Choice

A new planet, 'Planet Z,' is discovered with a G-force of 2.5G. If a 400 kg space probe lands there, predict its mass and how its weight would compare to its weight on Earth.

• Its mass remains 400 kg, and its weight is 2.5 times greater than on Earth.

• Its mass remains 400 kg, and its weight is the same as on Earth.

• Its mass becomes 1000 kg, and its weight is 2.5 times greater.

• Its mass becomes 160 kg, and its weight is 2.5 times less than on Earth.

Multiple Choice

Imagine you have two identical-sized boxes. When you lift them, Box A feels significantly heavier than Box B. Using your knowledge of mass and weight, analyze this situation.

• Box A must have more mass than Box B, which results in it having greater weight.

• Box A and Box B have the same mass, but the force of gravity is stronger on Box A.

• Box B must be hollow, while Box A is solid, but they have the same weight.

• The weight of both boxes is the same, but the mass of Box A is greater.

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Summary

Poll

On a scale of 1-4, how confident are you about the difference between mass and weight?

• 1

• 2

• 3

• 4