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Lesson

Measuring Matter

Everything around you - the air, your desk, even you - is made of matter. Scientists describe it with three measurements: mass, volume, and density.

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Driving Question
How can a giant steel ship float while a tiny pebble sinks?
🔬 Learning Science Focus 🔍 Phenomenon First 🏷️ Label After Learning 🪜 Stepwise Scaffolds ✏️ Generation Effect ✅ Retrieval Practice
📋 MA STE Standards · Grade 6 6.MS-PS1-7 (MA)
6.MS-PS1-7 (MA) Use a particulate model of matter to explain that density is the amount of matter (mass) in a given volume. Apply proportional reasoning to describe, calculate, and compare relative densities of different materials.
Learning Goals

What You'll Be Able to Do

By the end of this lesson, you will be able to:

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Define matter and explain how scientists measure it using mass (grams) and volume (cm³ or mL) with the right tools.
6.MS-PS1-7 (MA)
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Calculate the density of an object from its mass and volume, and use density to explain why objects sink or float.
6.MS-PS1-7 (MA)
Key Vocabulary

Words You'll Meet

Click a card to see what each word means. Click it again to close it. You'll meet every one of these in the lesson below.

Engage · Mystery

Three Objects. Three Puzzles.

Before you learn a single new word, think like a scientist about these three everyday objects. Click each card and consider the question.

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Two Same-Size Balls
A bowling ball and a beach ball can be exactly the same size, but one of them is much, much harder to lift.
If they take up the same space, what is different inside them?
Click to look closer
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The Invisible Stuff
Blow up a balloon and it gets bigger and slightly heavier. But you can't see anything inside it - just air.
Is air "stuff"? Does it really take up space and have weight?
Click to look closer
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The Floating Giant
A steel cargo ship has a mass of millions of kilograms, yet it floats. A pebble has almost no mass, yet it sinks instantly.
If heaviness decided floating, the ship should sink first. So what really decides?
Click to look closer
💡 One clue: none of these puzzles can be solved by one measurement alone. You need to compare how much "stuff" an object has with how much space it fills.
🤔 Scientists have exact words and tools for "amount of stuff" and "amount of space." By the end of this lesson, you'll use them to solve all three puzzles.
The question: Bowling balls, balloons, and cargo ships all follow the same rules of matter. This lesson is about learning to measure those rules.
Explore · The Big Idea

What Is Matter?

Look around you. Your desk, your water bottle, the air you're breathing - what do they all have in common?

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Think about it: A rock is obviously "stuff." But is air stuff too? Make a prediction.
The key idea

Matter is anything that has mass and takes up space (volume). That includes air! Air has mass (a filled balloon weighs slightly more than an empty one) and it takes up space (that's why the balloon gets bigger). The most common states of matter are solid, liquid, and gas.

Matter is everywhere, in all three common states:

🪨Rock - solid
🧊Ice cube - solid
💧Water - liquid
🥤Juice - liquid
🎈Air in a balloon - gas
💨Steam - gas
But "has mass and takes up space" raises a question: how do scientists actually measure those two things, with real numbers and real tools?

Let's find out.
Explore · Three Measurements

How Do We Measure Matter?

Scientists describe matter with three measurements. Follow the color coding through the whole lesson: teal is mass, green is volume, and orange is density.

Measurement 1
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Mass
Mass is the amount of matter in an object. It is measured in grams (g) with a triple beam balance.
Tool: Triple Beam Balance · Unit: g
Measurement 2
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Volume
Volume is the amount of space an object takes up. It is measured in cubic centimeters (cm³) with a ruler, or in milliliters (mL) with a graduated cylinder.
Tools: Ruler or Graduated Cylinder · Units: cm³ or mL
Measurement 3
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Density
Density is a measure of how much matter is packed into a space. It combines the first two measurements: mass ÷ volume.
Units: g/cm³ or g/mL
🧰 Pick the Right Tool
A real scientist's first decision is choosing the right tool and unit. Answer all three to prove you're lab-ready.
1. You need to measure the mass of a wooden block. Which tool do you grab?
2. You need to measure the volume of juice for an experiment. Which tool do you grab?
3. You need the volume of a rectangular block (a solid with straight sides). Which tool do you grab?
🏆 Three for three! Mass → triple beam balance (g). Liquid volume → graduated cylinder (mL). Block volume → ruler (cm³). You're lab-ready.
The ruler trick: how does measuring length, width, and height with a ruler give you a volume? Let's build a block and see the math happen live.
📦 Volume Block Builder
Drag the sliders to resize the block. Volume = length × width × height. Watch the block and the math change together.
Length 5 cm
Width 2 cm
Height 1 cm
V = length × width × height V = 5 × 2 × 1 = 10 cm³
You now have two of the three measurements. Mass tells you how much matter. Volume tells you how much space. The third measurement - density - is where the floating-ship mystery gets solved.
Explain · Packing It In

Density: The Ratio of Mass to Volume

Remember the bowling ball and the beach ball? Same size, totally different heft. Density is the measurement that explains why.

The key idea

Density is the ratio of mass to volume: how much matter is packed into a space. It can be measured two ways: in g/cm³ (triple beam balance + ruler) or in g/mL (triple beam balance + graduated cylinder).

🎳 Bowling ball: lots of mass packed into its volume → high density.
🏖️ Beach ball: almost no mass spread across the same volume → low density.
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Density Lab: Water has a density of 1 g/mL. You're about to build an object and drop it in a tank. What do you think decides whether it floats? Make a prediction to unlock the lab.
🎛️ The Density Lab
Drag the sliders to set your object's mass and volume. The lab calculates the density live and drops the object into a tank of water (density = 1 g/mL).
Mass 50 g
Volume 100 mL
The Math
D = 50 g ÷ 100 mL
D = 0.5 g/mL
The Tank (water = 1 g/mL)
✓ Floats - density below 1 g/mL
That's the answer to the ship mystery. Floating isn't decided by mass alone - it's decided by density. A steel ship is huge and full of air, so its overall mass divided by its enormous volume comes out below 1 g/mL, and it floats. A pebble is small but tightly packed, so its density is well above 1 g/mL, and it sinks.
Sliders are easy - now do it like a scientist. In the lab you get a balance, a ruler, and an unknown block. Time to calculate density by hand, step by step.
Explain · Worked Example

Calculating Density, Step by Step

Watch one problem solved completely. Then you solve the next one yourself, with the same two steps every time.

📐 Worked Example
A block has a mass of 50 g. You measure it with a ruler: 5 cm long, 2 cm wide, 1 cm tall. What is its density?
Mass = 50 g Dimensions = 5 cm × 2 cm × 1 cm
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Find the volume. A ruler gives you dimensions, not volume - so multiply them. V = length × width × height = 5 × 2 × 1 = 10 cm³
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Use the density formula. Divide mass by volume. D = m ÷ V = 50 g ÷ 10 cm³ = 5 g/cm³
Sanity check: 5 g/cm³ is much denser than water (1 g/cm³), so this block would sink. Always ask whether your answer makes sense.
✏️ Your Turn: Density Practice Problem
You have a wooden block with a mass of 60 grams. You measure it with a ruler: 4 cm long, 3 cm wide, and 2 cm tall. What is the density of the wooden block?
Mass = 60 g Dimensions = 4 cm × 3 cm × 2 cm
1
Find the volume. V = length × width × height = 4 × 3 × 2 = ?
2
Use the density formula. D = m ÷ V = 60 g ÷ 24 cm³ = ?
🏆 You did it! Density = 60 ÷ 24 = 2.5 g/cm³. That's denser than water, so this "wooden" block would sink - it must be a very dense wood, like ebony. You just calculated density exactly the way a scientist does.
Quick Recall
Just a quick brain check before we move on. Not graded.
Two cubes are exactly the same size. Cube A has a mass of 270 g, and cube B has a mass of 27 g. Which statement is true?
Elaborate · Wrap-Up

Back to the Floating Giant

You started this lesson with three puzzles: same-size balls with different heft, invisible air, and a steel ship that floats. Now you can solve all three.

The Answer
The ship floats because its density, not its mass, is less than water's.
A ship's hull is mostly air, so its total mass divided by its huge volume comes out below 1 g/mL. The pebble's matter is tightly packed, so its density is far above 1 g/mL - down it goes.
The Three Measurements
Every piece of matter can be described with the same three numbers.
No matter the object, the measurements are:
Mass · g Volume · cm³ or mL Density · m ÷ V
The Other Two Puzzles
Same volume, different mass = different density.
The bowling ball packs far more matter into the same volume as the beach ball - that's density. And air? It has mass and takes up space, so air is matter too, just a gas with very low density.
Quick Recall
One more brain check. Not graded.
An ice cube floats in a glass of water. What must be true about the ice?
Evaluate · Lesson Summary

Key Vocabulary & Learning Goals

Everything from this lesson in one place: the words to know and the goals you worked toward.

TermStudent-Friendly Definition
MatterAnything that has mass and takes up space (volume). The most common states are solid, liquid, and gas.
MassThe amount of matter in an object, measured in grams (g) with a triple beam balance.
VolumeThe amount of space an object takes up, measured in cm³ with a ruler (V = l × w × h) or in mL with a graduated cylinder.
DensityHow much matter is packed into a space: the ratio of mass to volume (D = m ÷ V), in g/cm³ or g/mL.
Triple beam balanceThe lab tool used to measure mass in grams.
Graduated cylinderThe marked container used to measure liquid volume in milliliters.
Learning GoalsHow You Showed It
Define matter and explain how scientists measure it using mass and volume with the right tools (6.MS-PS1-7 MA). You predicted whether air is matter, matched tools to measurements, and built block volumes with V = l × w × h.
Calculate density from mass and volume and use it to explain sinking and floating (6.MS-PS1-7 MA). You ran the Density Lab, solved a two-step density problem by hand, and explained why a steel ship floats while a pebble sinks.
Essential question: How can a giant steel ship float while a tiny pebble sinks? If you can answer that with the words mass, volume, and density, you own this lesson.
Quiz

Check Your Understanding

Five questions covering everything you discovered, including a density problem to solve. Answer every question, then submit.

Your score will not be sent Your score will be sent to your teacher
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🔍 The Mystery You Came In With You started this lesson with one question: "How can a giant steel ship float while a tiny pebble sinks?" If you can explain it using mass, volume, and density, you've solved the mystery.
Go Further

More Learning

Measuring matter is the foundation of all of chemistry. Extension challenges: find the density of an irregular object at home - measure its mass on a kitchen scale, then drop it into a measuring cup of water and see how many milliliters the water rises (that rise IS its volume). Or rank five household objects from least to most dense, then test your ranking in a sink of water.

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Lesson
Building Blocks of Matter
You measured matter from the outside. Now zoom in: what is matter actually made of? Meet atoms and molecules, the particles that explain why density even exists.
Continue
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Lesson
Pure Substances and Mixtures
Density is a fingerprint: every pure substance has its own. Discover how scientists use properties like density to tell pure substances and mixtures apart.
Continue
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Lesson
Physical Properties
Density is just one physical property. Explore color, hardness, melting point, conductivity, and the full toolkit scientists use to describe and identify matter.
Continue