الأسبوع 8 · المحور 1، الباب 3 «الجسم السليم والطعام الصحي» (ج): حفظ الطعام باردًا وخطة المقصف · 3 دروس
2
Build and test a cold box
Discover P3 Term 1: Axis 1, Chapter 3
GoalPlan a fair test of materials for a cold box, record the results, rank the materials and choose one for the canteen.
New words
fair test · a test where only one thing changes and all the rest stays the samematerial · what something is made of, such as cloth, paper or foilmelt · to change from ice into waterresults · what we find out from a test
Explanation
Engineers follow steps: ask, imagine, plan, build, test and improve. To test cold boxes, we need a fair test. We change only one thing: the material of the box. Everything else stays the same: the size of the ice cube, the sealed bag, the box size, the place and the time. A grown-up helps with this test. Put one ice cube from water in a sealed sandwich bag inside each box. Put all the boxes in a warm place for 40 minutes. We never look at the Sun. Then take out each bag and measure how much has melted. Less melted water means the box kept the ice colder. Write the results in a table or bar graph, rank the materials from best to worst, and use the evidence to choose a material for the canteen.
ask→imagine→plan→build→test→improve
Worked examples
Fair or unfair? Farida puts a big ice cube in the cloth box and a small one in the foil box. This is unfair, because the size of the ice changed too. Both boxes must hold ice cubes of the same size.
Example results after 40 minutes (a grown-up measured the meltwater in spoonfuls). Cloth box 3, newspaper box 5, foil box 8, no box 11. The cloth box is best because the least ice melted.
Rank
Box
Spoonfuls melted
1
Cloth
3
2
Newspaper
5
3
Foil
8
4
No box
11
Ranking from best to worst: 1 cloth box, 2 newspaper box, 3 foil box, 4 no box. The no-box bag melted 11 − 3 = 8 spoonfuls more than the cloth box.
Class activity
Cold box test, with a grown-up. Make three small boxes from the same size of cardboard box, each lined with a different material. Prepare a fourth bag with no box. Put one ice cube (from water) of the same size in a sealed bag in each. Leave them in a warm place for 40 minutes. Do not look at the Sun. Then measure the meltwater with a spoon. Rank the materials and write which one you would use for the canteen and why. Wash hands after.
Practice
1
Why must the ice cubes all be the same size?
So the size of the ice does not change the result; only the box material should be different.
2
Name two things that must stay the same.
For example: the size of the ice cube, the time, the place, the bag.
3
Look at the results. Which box kept the ice coldest?
The paper box: it had the fewest spoonfuls melted (4).
4
In the same results, how many more spoonfuls melted in the plastic box than in the paper box?
