Engineering Design
Defining the problem
An engineering problem is stated with criteria and constraints. Criteria are the goals: what the design must do to succeed, such as “hold 100 grams across a 20-centimeter gap.” Constraints are the limits: time, money, available materials, safety rules, and size. A common trap is confusing the two, or ignoring a constraint such as “only one sheet of paper allowed.”
Generating and comparing solutions
Good engineers produce several possible designs before building. Comparing them means listing how well each meets the criteria and stays within constraints - not simply picking the most attractive or complicated one. Failure is useful information: a design that collapses tells you where to add strength.
Fair tests
A fair test changes one variable at a time and keeps everything else the same: same span, same support, same method of loading. Repeat trials and average them, because a single result is unreliable. Measure with tools and record data in a table. If you change two things at once, you cannot tell which one caused the result - a very common trap in these questions.
Improving a design
After testing, identify the weakest part, change one feature, then retest and compare. Improvement is a cycle: define, design, build, test, improve.
Worked example
Building a paper bridge: criteria are “span 20 cm and hold 100 g”; constraints are “one sheet of paper plus 10 cm of tape.” The fair test measures grams held, adding mass in equal steps until failure, repeated three times. Adding a different amount of tape each time would make the results impossible to compare.
Rule of thumb
Change one thing; measure the same thing; repeat.