3
The best material for the job
Workbook 2: Topic 3.4, pp. 38–40
GoalUse test results to choose the best material for a job and give a reason.
New words
best · better than all the othersevidence · what the results of a test showconclusion · what you decide from your results
Explanation
We use test results as evidence to choose the best material. Look at Sara’s waterproof test. A rain cover must keep water out, so we choose a waterproof material, such as plastic or foil. Look at Yuki’s absorbent test. A cloth for wiping spills must soak up water, so we choose the sponge. Different jobs need different properties. We say: I choose this material because the test showed that it … This is a conclusion. If the results do not seem right, we can do the test again.
| Job | Best material | Evidence |
|---|---|---|
| rain cover | plastic bag | towel stayed dry |
| wipe up spills | sponge | soaked up 8 spoonfuls |
Worked examples
A cover for the picnic basket must be waterproof. A plastic sheet is best because it kept the towel dry.
To mop a spill, Omar picks a sponge, because it soaked up the most water.
To wipe a wet window, a plastic bag only pushes the water around. A sponge or a cloth is a better choice because it is absorbent.
Class activity
Choose and explain (with an adult): think of three jobs, such as covering a bicycle seat in the rain, drying a plate and wiping a table. For each, choose the best material from the ones you tested. Say why, using the words “because the test showed…”.
Practice
1
Which material is best to cover a bicycle seat in the rain?
The plastic bag, because it is waterproof.
2
Which material from Yuki’s test would you NOT use to dry a wet dog? Why?
The plastic bag. It soaked up no water at all.
3
Finish the sentence: A good raincoat needs to be ...
waterproof.
4
Ana needs a bib that soaks up spilled milk. Use her results to choose a material.
| Material | Spoonfuls soaked up |
|---|---|
| plastic | 0 |
| cotton | 6 |
| foil | 0 |
Cotton, because it soaked up the most (6 spoonfuls). It is absorbent.