Density

Density

Middle School

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Learning Objectives

Key Vocabulary

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Density

Density is the amount of matter in a given space, or the ratio of mass to volume.

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Mass

Mass is a measure of the amount of matter an object contains and is not affected by gravity.

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Volume

Volume is the amount of three-dimensional space that an object or substance occupies or contains within.

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Water Displacement

A method for measuring the volume of an irregularly shaped object by submerging it in water.

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What is Density?

• Density is how much mass is packed into a certain amount of volume.

• A golf ball is denser than a table tennis ball, which makes it heavier.

• Objects that are less dense than water, like logs, will float on the surface.

• A material's density is the same no matter how much of it you have.

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Multiple Choice

Which of the following best describes why a large log floats in a river?

• The log is heavier than the water.

• The log has a larger volume than the water.

• The log is an intensive property.

• The log is less dense than the water.

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The Building Blocks: Mass and Volume

Mass

• ​Mass is the measure of the amount of matter or 'stuff' in an object.

• ​​It is commonly measured in units such as grams (g) or kilograms (kg).

• ​An object’s mass stays the same and is not affected by gravity or location.

Volume

• ​Volume is the amount of space that an object or a substance occupies.

• ​​Units include cubic centimeters (cm³), cubic meters (m³), and milliliters (mL).

• ​For measurement, one cubic centimeter is equal to one milliliter (1 cm³ = 1 mL).

Multiple Choice

Which statement about mass is correct?

• Mass changes when an object moves to a place with less gravity.

• Mass decreases on the Moon but increases on Earth.

• Mass depends on how fast an object is moving.

• Mass is measured in units like grams and kilograms.

How to Measure Volume

Multiple Choice

A student needs to find the volume of a small, oddly shaped stone. What is the correct method to use?

• Calculate it by reading the top of the meniscus.

• Use the water displacement method with a graduated cylinder.

• Place it on a scale to find its mass.

• Measure its length, width, and height with a ruler.

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Calculating Density

Multiple Choice

If a rock has a mass of 150 g and a volume of 50 cm³, what is its density?

• 0.33 g/cm³

• 100 g/cm³

• 7500 g/cm³

• 3 g/cm³

Why Things Sink or Float

• An object sinks or floats based on its density compared to the fluid.

• Objects denser than water sink, while less dense objects float.

• Sinking objects have tightly packed particles; floating objects have spaced-out particles.

Multiple Choice

An object has a density of 1.4 g/mL. What will happen when it is placed in a container of pure water (density 1.0 g/mL)?

• It will hover in the middle of the water.

• It will dissolve in the water.

• It will float on the surface.

• It will sink to the bottom.

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Density in Action: Calculations

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Multiple Choice

What is the mass of a 10 cm³ block of copper if its density is 8.92 g/cm³?

• 1.12 g

• 0.892 g

• 18.92 g

• 89.2 g

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Common Misconceptions About Density

Misconception	Correction
Heavy objects always sink.	Sinking depends on density, not just weight. A heavy ship can float.
Mass and weight are the same thing.	Mass is the amount of matter. Weight is the force of gravity.
Large objects are denser than small objects.	Density is mass per unit of volume, not a measure of size.
Ice is denser than water because it is solid.	Ice is a rare solid that is less dense than its liquid form.

Multiple Choice

How does the arrangement of particles explain why a block of aluminum (density 2.70 g/cm³) is denser than a block of ice (density 0.92 g/cm³)?

• The particles in aluminum are larger than the particles in ice.

• The particles in aluminum are more tightly packed for the same amount of space than in ice.

• The particles in aluminum are more spread out than in ice.

• The particles in aluminum are lighter than the particles in ice.

Multiple Choice

A scientist observes that a balloon filled with a gas rises in the air. What can be concluded about the gas inside the balloon?

• The gas is less dense than the surrounding air.

• The gas has a smaller volume than the air.

• The gas has a greater mass than the air.

• The gas is denser than the surrounding air.

Multiple Choice

You drop a 27g object into a graduated cylinder with 50 mL of water, and the water level rises to 60 mL. What is the object's density, and will it sink or float in mercury (density 13.6 g/mL)?

• Density is 0.45 g/mL; it will sink in mercury.

• Density is 0.45 g/mL; it will float in mercury.

• Density is 2.7 g/mL; it will float in mercury.

• Density is 2.7 g/mL; it will sink in mercury.

Multiple Choice

An oil spill occurs at sea. Based on the principle of density, predict the immediate effect and explain why this happens.

• The oil will sink to the ocean floor because it is heavier than water.

• The oil will float on the surface of the water because it is less dense than water.

• The oil will evaporate immediately upon contact with water.

• The oil will mix evenly with the water because they have similar densities.

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Summary

Poll

On a scale of 1-4, how confident are you about calculating an object's density?

• 1

• 2

• 3

• 4