Engineering Design: Criteria, Constraints, and Optimization
The Engineering Design domain tests how well you can define a problem, develop possible solutions, and optimize a design using evidence. Questions often present a design scenario with criteria, constraints, and test data, then ask you to identify the best next step, explain a trade-off, or justify a redesign.
Core rules
- A design problem has criteria, which state what the solution must do, and constraints, which are limits such as materials, cost, time, or size.
- Engineers build and test prototypes, collect data, and compare results with the criteria. Testing one variable at a time makes results easier to interpret.
- Optimization means improving a design while balancing trade-offs: a change that improves one criterion may worsen another or violate a constraint.
- Failure is useful data. A design that does not meet criteria should be analyzed and revised, not accepted because it is the first attempt.
Worked example
A team must build a paper bridge spanning 20 cm and holding 500 g using at most three sheets of paper. A flat bridge holds 200 g. Folding the paper into corrugations raises capacity to 450 g. Adding side beams raises it to 700 g but uses four sheets.
Reasoning: the span and load are criteria; the three-sheet limit is a constraint. The corrugated design improves strength but still misses the load criterion. The side-beam design meets the load but violates the material constraint, so it cannot be accepted as is. The next step is to redesign within three sheets, for example by adjusting corrugation shape or beam placement, and retest. The team should not ignore the constraint just because the bridge holds more mass.
Traps that cost marks
- Choosing a design that meets the load but violates a stated constraint.
- Changing several variables at once and then claiming one change caused the improvement.
- Treating a single test as conclusive.
- Describing a prototype as a final product without iteration.