Testing and analysing designs
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課程筆記
The Frozen Pipes Problem
- The engineering task: a cabin in Utah's Uinta Mountains gets very cold in winter, and if it is left without heat, the water pipes inside can freeze and burst.
- The challenge is to design, construct, and test a device that affects the rate at which the water in the pipes freezes.
- Before designing a solution, engineers identify the criteria (the positive outcomes they want) and the constraints (the limits they must design within).
- This is an engineering design task: the goal is not just to build one device, but to test several competing designs, compare their data, and combine the best features of each into an improved solution.
A cabin in Utah's Uinta Mountains, whose water pipes may freeze in winter
Criteria and Constraints
- Criteria are the positive outcomes a design should achieve — for the frozen-pipes problem, keeping the water from freezing for as long as possible is a criterion.
- Constraints are the limits a design must fit within, such as a budget, a maximum size or weight, or how easy the materials are to work with.
- Before comparing designs, engineers list the research questions this raises: what materials are available, what do they cost, and what limits apply to the finished device?
- A design that meets every criterion but breaks a constraint — for example, costs far more than the budget allows — is not an acceptable solution.
Researching and Developing Possible Designs
- Once the criteria and constraints are clear, engineers research possible solutions — for example, comparing different materials that might slow the freezing of the pipes.
- Developing possible designs takes imagination as well as reasoning based on what the research found.
- Most problems have more than one reasonable design — this is why testing and comparing competing designs matters.
- Each candidate design is a hypothesis about what will work; only testing can show whether it actually meets the criteria.
Building and Testing a Model
- A model of each design is built and tested before a final version is produced.
- Testing is what allows problems with a design to be found and fixed early, rather than after the device is finished.
- Every design should be tested under the same conditions so the results can be fairly compared — for example, the same starting temperature and the same length of time.
- The result of a test is data: a measurement, such as how long a pipe stayed above freezing, that can be compared across designs.
Analysing Test Data to Compare Designs
- When several designs are tested, the next step is to analyse the data to find the similarities and differences between them.
- Comparing data might show that one design kept water warm for longer, another was cheaper, and a third was easiest to install.
- Analysing the data identifies the best characteristics of each competing design — not just which design is best overall.
- A conclusion drawn from test data should be based only on what the data actually shows, not on which design looks the most impressive.
Combining the Best Features into a New Solution
- The engineering design process does not stop at picking a single winning design — the best characteristics of each competing device can be combined into a new solution.
- For example, if one design's material was the most effective at slowing freezing and a different design's shape was the cheapest to build, a new design could combine both features.
- Combining features usually produces a solution that meets the criteria and constraints better than any one of the original designs did alone.
- This is the heart of the engineering design standard for this task: compare, identify the best of each, and combine.
Modifying and Retesting
- After testing and analysing the data, a design is usually modified to fix problems the test revealed or to add a strength borrowed from another design.
- The modified design is then retested to check whether the change actually improved performance.
- This test-analyse-modify cycle repeats until a design meets its criteria while staying within its constraints.
- Only once a design passes this cycle is it shared as a finished solution to the problem.
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練習題
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1.A student compares two pipe-freezing prevention designs by wrapping them around identical pipes filled with hot water and timing how long each stays above freezing. Which variable must be kept the same for this to be a fair test?
Easy- AThe starting temperature of the water
- BWhich design is tested first
- CThe name given to each design
- DThe colour of the wrapping material
2.In a fair test comparing two competing designs, only the one feature being tested should be different between them.
EasyTrue or false?
3.When designing a device to prevent pipes from freezing, which of the following are constraints that should be considered? (select all that apply)
Medium- ABudget limit
- BMaximum size or weight
- CEase of installation
- DThe colour of the insulation
- EThe brand name of the pipes
4.Two designs are tested for how long they keep water above freezing. Which of these is a criterion for this test, rather than a controlled variable?
Medium- AKeeping the water above freezing for as long as possible
- BUsing the same amount of water for each design
- CTesting each design for the same length of time
- DStarting each test at the same water temperature
5.If two competing designs are tested with a different amount of water in the pipe, the results can still be compared fairly.
EasyTrue or false?
6.Three pipe-freezing prevention designs are tested under the same conditions. The results are: | Design | Time above freezing | |---|---| | A | 40 minutes | | B | 55 minutes | | C | 48 minutes | Based on this data, which design performed best at the test's main goal?
Easy- ADesign B
- BDesign A
- CDesign C
- DCannot be determined from the data
7.A design is tested with three different thicknesses of the same insulating material, keeping every other condition the same: | Thickness | Time above freezing | |---|---| | 1 cm | 40 minutes | | 2 cm | 55 minutes | | 3 cm | 68 minutes | What conclusion is best supported by this data?
Medium- AIncreasing the thickness increased the time the water stayed above freezing.
- BThickness had no effect on the time the water stayed above freezing.
- CIncreasing the thickness decreased the time the water stayed above freezing.
- DThe results are too different to draw any conclusion.
8.Three designs (A, B, C) are tested for how much the water temperature drops after 15 minutes: A drops 12°C, B drops 8°C, C drops 15°C. Which conclusions are supported by this data? (select all that apply)
Medium- ADesign B lost the least heat.
- BDesign A lost less heat than Design C.
- CDesign C lost the most heat.
- DDesign A lost less heat than Design B.
- EAll three designs performed the same.