Identifying Materials by Property

Step 1: Something to Notice

Watch first. The explanation comes later.

Watch the idea first — 43 seconds. Then read on, and try it yourself in the next step.

Two gray bars, identical to look at. One floats in water and one sinks. One sticks to a magnet and one does not.

What tests would tell you what a material actually is?

Step 2: Find Out

Try each material and record what the test says rather than what it looks like.

Step 1 — Predict

Two bars look identical. Can you tell what they are made of by looking?

Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.

Step 3: So Here Is Why

Now the explanation, after you have seen it happen.

A property is something about a material you can measure or test rather than argue about: whether it floats, whether a magnet pulls it, whether it conducts electricity, how much a set volume of it weighs. Anybody repeating the test gets the same answer.

Property Something about a material you can measure or test.

Useful properties

Whether it floats, whether a magnet pulls it, whether it lets light through, whether it conducts.

Appearance is not a property test

Aluminum and steel look the same. Only a test separates them.

Use more than one test

One result rarely picks out a single material. Two or three together usually do.

What it is made of, not what it looks like

Two objects can look identical and be different materials. Density, hardness, magnetism, how it conducts and what it dissolves in are properties that identify a material regardless of shape or color.

Use more than one property

Several materials share any one property. Testing two or three narrows it down much faster, in the same way two clues identify a person better than one.

Step 4: A Common Mistake

Lots of people think

“You can tell what something is made of by looking at it.”

Step 5: How Recycling Plants Sort Metal

The same idea somewhere new.

Scrap is sorted by property, never by eye. A magnet lifts out the steel. An eddy-current machine flings the aluminum sideways. What is left goes by density. Three measurable properties, no looking, and it works at hundreds of tonnes an hour.

Sorted by property

Step 6: Think It Through

Practice makes it stick.

Two Gray Bars

Problem 1 of 1

Two identical-looking gray bars. Which test separates aluminum from steel?

Testing Materials

1 of 4

What is a property?

2 of 4

Which of these are properties you can test?

3 of 4

Can you identify a material by looking?

4 of 4

Why use more than one test?

Step 7: Quick Check

Show what you know.

Question 1 of 1

How do you find out what a material is?

Step 8: Explain It in Writing

Claim, evidence, then reasoning.

The question

You ran the tests on the unknown sample one at a time and watched the list shrink. Write an argument answering the question: was one test enough to say what the sample was made of?

Evidence you can use

Before any test, all four materials were still possible: oak wood, glass, aluminum and steel.
The density test read between 1 and 5, which ruled out oak wood and steel and left two.
The magnet test read no pull, and two materials were still possible. It ruled nothing new out.
The light test read blocked, which ruled out glass and left only aluminum.
Glass and aluminum both sit in the density band between 1 and 5, so density cannot separate them.
I used the same sample for all three tests and only changed how many tests had been run.
The sample was a plain gray block, and it looked like it could have been steel.

Words to usepropertytestruled outstill possibledensitymagnet

ClaimOne sentence that answers the question.EvidenceWhat you saw or measured that supports it.ReasoningWhy that evidence supports your claim. This is the part most people leave out.

Fill in all three boxes. The reasoning box is the one that matters most.

What You Found Out

A property is something about a material you can measure or test.
Floating, magnetism and letting light through are all properties.
Appearance is not a test — two materials can look identical.
Use more than one test to identify a material.