Engineering MakingPicking the Right Material for the Job
Atlas stands outside beside a small model house, holding a metal sheet in one gloved hand and a sponge in the other, looking up at rain clouds gathering in the sky with a curious, thinking expression on his face.
- Identify at least two properties of materials, such as waterproof or soft.
- Explain why the properties of a material matter when choosing it for a job.
- Compare two different materials and decide which one is better for keeping out rain.
- Predict what would happen if the wrong material were used for a job.
Key terms
- material
- what something is made of, like wood, metal, cloth, or plastic
- property
- a word that tells what a material is like, such as hard or waterproof
- waterproof
- a property where water rolls off instead of soaking in
- absorb
- to soak up water like a sponge or paper towel does
Materials Have Properties
A property is a word that tells us what a material is like. Some materials are hard, like metal. Some are soft, like a sponge. Some are stretchy, like a rubber band. One important property is whether water soaks in or rolls off. Knowing the properties of each material is the first step engineers take. Once you know what a material is like, you can decide where it belongs in a build.
Match the Material to the Job
Engineers do not pick materials by accident. They first ask what the material needs to DO. A roof needs to keep rain out, so the job is to be waterproof. Then they pick a material whose properties match that job, like metal or plastic. A sponge soaks up water, so it would let the rain right in. Matching the right property to the right job is the smart engineer way to build.
Worked examples
You are choosing a material for a roof that must keep rain out. How do you pick the right one?
- Name the job the material must do: keep rain out of the house.
- Decide which property matters most: being waterproof.
- Check each material to see if water rolls off or soaks in.
- Pick metal or plastic, because water rolls off them and they are waterproof.
Answer: Choose a waterproof material like metal or plastic, because water rolls off it and keeps the inside dry.
Activity
Help Atlas sort each material — drag it to the bin that matches what it does with water.
Practice
Name two waterproof materials and explain why they keep rain out.
Pick a job like making a soft pillow, then choose a material whose property fits.
Common mistakes to avoid
- A material's color tells you its job.A property like waterproof or soft tells you the job, not the color of the material.
- Any soft material works as a roof.A roof needs a waterproof material, and many soft materials like sponges soak up water instead.
Check your understanding
You are building a roof for a doghouse. It rains a lot where you live. Which material is the BEST choice for the roof?
Atlas says engineers pick a material by looking at its properties. What does a property tell you about a material?
Mia used a paper towel as a roof on her model house. It rained and the inside got all wet. What went wrong?
Recap
A material is what something is made of, and every material has properties like hard, soft, or waterproof. Engineers first ask what job the material must do, then pick the one whose properties match. For a roof that keeps rain out, they choose a waterproof material like metal or plastic, not a sponge.
Reflect
What property would you look for when choosing a material for rain boots?