Test It, Don't Guess It: Properties of Everyday Materials

We are learning to run fair tests on everyday materials and record the results in a properties table that we can use as evidence when we choose materials.

Before you startAbout 85 minutes · what success looks like · notes for the helper

About 85 minutes. It's fine to stop after the Quick Check and come back another day: the lesson opens where you left it, at the Quick Check.

You'll know you've got it when

I can define stiffness, compressive strength, tensile strength, water resistance and mass in my own words and say what each test measures
I can plan a fair test by naming what I change, what I measure and everything I keep the same
I can repeat a test three times, work out the mean and record it with its unit in a properties table
I can read a properties table and choose a material for a stated job, giving the number that justifies it

For the helperhow to sit beside this lesson, and what this step is for

This step: Spark

Start with the question at the top and chat about it. There is no wrong answer here: it gets your learner thinking about what they already know.

Getting ready: Five small samples to test: a strip of cereal-box card, a strip of corrugated cardboard, a clean offcut of untreated solid timber (never treated pine, which carries preservative chemicals, or MDF, whose fine dust is harmful to breathe) that has been sanded smooth, a fabric scrap and a clean plastic container (an adult cuts the plastic). A ruler, a few coins, a teaspoon, a tray, kitchen scales, a cushion and a clamp for the stretching test (a G-clamp or spring clamp; if you have none, an adult can hold the strip's end flat under both hands on the table) are all the equipment the tests need. Five properties with three trials each take the lesson to about 85 minutes, a lot for one sitting, so spreading the tests over two sittings is reasonable, with the break after the check.
What understanding sounds like: Listen for your young person naming what was changed and what was kept the same ('same width, same overhang, same coins') and for a claim tied to a number, such as 'corrugated drooped 7 mm and card drooped 36 mm'. A claim that begins with 'I think' and has no number is a good moment for a gentle question.
A likely mix-up, and something that helps: The common belief is that the strongest or toughest material is simply the best one, and that 'strong' is one thing. You might ask, 'Strong in which direction, and does this job even need strength?' A strip that stands up to squashing can still fold easily when it is bent, and your young person's own results can show it.
If it comes easily: If it comes easily, you might ask for a second variable to be tested on one material, such as thickness or the direction the corrugations run, and for a prediction with a number before testing.
If it's a struggle: If it is a struggle, one way is to test just two materials on one property, such as bending, do the three trials together, and write the plan as three short lines: change, measure, keep the same.

Step 1 of 6 · Spark

Lesson 1 of 5 · Choosing Materials That Do the Job

Same box, two jobs

For the helper

Start with the question at the top and chat about it. There is no wrong answer here: it gets your learner thinking about what they already know.

A cardboard box can carry five kilograms of books sitting on its base without the bottom bulging. Pick the same box up by its top flaps and the flaps tear in seconds. Same box, same cardboard, same books. One job it does well and the other it fails at. So is cardboard strong or weak? The honest answer is that the question is unfinished. Strong against being squashed, from which direction, for how long, and does the job even need that? Designers cannot work with 'strong' or 'good' or 'sturdy'. They need to know what a material does when it is bent, squashed, stretched or wet, as a number they can compare. That is what a test gives you, and this lesson is where you build that evidence.

Same cardboard, two different jobs: it carries the load from the base and tears when carried from the flaps.