Week 23 · Theme 3 Protecting Our Planet, Unit 3 Our Earth’s Resources: Interdisciplinary Project Water by the Sea (B) · 3 lessons
3
Test, improve and present
Discovery Education Science P5: Term 2, Unit 3, pp. 97–98
GoalTest a still without drinking the water, read the results, suggest improvements and present the design.
New words
test · a trial that shows whether a design worksimprove · to change a design to make it work betteranalysis · looking carefully at results to see what they mean
Explanation
A design is not finished until it is tested. Because the water is never tasted or drunk, we ask other questions. How much water did the cup collect? We measure it in millilitres. Does the collected water look clear? Did the salt stay in the bowl? To check for salt without tasting, a grown-up dips a clean spoon into the collected water and lets it dry in the sun: white crystals mean salt got in. If your still did not work well, do not be upset. Engineers expect problems, write them down and fix one at a time. A darker bowl may warm faster, a bigger surface lets more water evaporate, and a better seal stops vapour escaping. After testing, the team looks at what worked, what did not and what could work better. The reporter then presents the blueprint, the results and the improvements.
Worked examples
Time
Water in the cup (mL)
12:00
15
13:00
28
14:00
40
The graph shows one team’s still on a sunny day. By 12:00 it had 15 mL and by 14:00 it had 40 mL. In the last two hours it collected 40 − 15 = 25 mL. More water came in the middle of the day because the Sun was strongest.
Team A collected 40 mL and Team B collected 55 mL. B collected 55 − 40 = 15 mL more. The team asks why: B used a dark bowl and sealed the edge better. They change only one thing next time to learn which one matters.
problem→design→results→improvements
A safe presentation has four parts: the problem, the design, the results and the improvements. The reporter says, “We wanted fresh water from salt water. Our still collected 55 mL in four hours. Next time we will seal the edge better.”
Class activity
Build, test and report (a grown-up helps; outdoors, with hats and shade). Pour 500 mL of salty water into a wide bowl. Stand a small clean cup in the middle. Cover the bowl with plastic wrap and tape it down, and put a clean weight on the wrap above the cup. Leave it in the sun for three or four hours. A grown-up lifts the wrap and pours the collected water into a measuring jug. Write how many mL you collected. Dip a clean spoon in the collected water and let it dry: are there crystals? Do not drink or taste it. Then write one change for next time.
Practice
1
Why do we not taste the collected water to check whether it is fresh?
Tasting is unsafe. The water could still hold salt or germs, so we measure and use the spoon test instead.
2
Look at the graph. How much water was in the cup at 13:00 and how much more arrived by 14:00?
28 mL at 13:00; 40 − 28 = 12 mL more.
3
A still collected 36 mL in the first 3 hours and 24 mL in the next 2 hours. How much is that altogether?
36 + 24 = 60 mL.
4
Name two changes that could make a solar still collect more water.
Any two: a darker bowl, a bigger surface, a tighter seal, more hours in strong sun.
