Engineering MakingSharpen the Problem: Criteria and Constraints
Atlas the steady guide stands at a workshop whiteboard, sketching a fuzzy complaint and crossing it out beside a clean labeled problem statement, with sticky notes, a ruler, a small budget jar, and a stopwatch on the table.
- Define criteria and constraints in your own words.
- Rewrite a vague need into one precise, testable problem statement that names the user, the need, the criteria, and the constraints.
- Sort given details into criteria versus constraints.
- Identify why a measurable criterion beats a vague feeling like 'better'.
- Explain how scientific principles and environmental impact shape the limits an engineer must respect.
Key terms
- Problem statement
- One sentence naming user, need, criteria, and constraints
- Measurable criterion
- A success goal stated with a number or test
- Constraint
- A limit on cost, materials, time, or safety
- Need
- The real-world problem a user wants solved
From Complaint to Statement
A raw need like 'my backpack hurts' is only a feeling, and feelings cannot be designed for directly because no one can tell when they are satisfied. The engineer's first move is to translate that complaint into a sharp problem statement that names the user, the need, the measurable criteria, and the constraints, turning a vague gripe into a target a whole team can aim at and later test against.
Constraints Keep Designs Responsible
Constraints are more than budget and size limits. They include scientific principles you cannot break, like gravity and heat transfer, and real-world impacts such as harm to people or the environment. Treating these as hard boundaries is not pessimism; it keeps a clever idea realistic and ethical, so the finished design actually works in the physical world and does not create new problems while solving the original one.
Worked examples
Turn the complaint 'this water bottle leaks in my bag' into a four-part problem statement.
- Name the user and need: a student needs a bottle that does not leak in a backpack.
- Add a measurable criterion: stays sealed with no drips when held upside down for 30 seconds.
- Add constraints: holds at least 600 milliliters, costs under $8, made from food-safe recyclable material.
Answer: A student needs a leak-proof bottle that stays sealed upside down for 30 seconds, holds 600 mL, costs under $8, and uses food-safe recyclable material.
Activity
Sort each detail about a redesigned water bottle into Criteria or Constraints.
Practice
Rewrite 'my chair is uncomfortable' as a measurable success criterion.
Sort six water-bottle details into criteria versus constraints and explain one.
Common mistakes to avoid
- Comfortable is a good criterionComfort is a feeling with no measurement, so a stronger criterion gives a number like a support angle you can check.
- Numbers always mean criteriaA numeric limit on materials or time is a constraint, because it is a boundary you cannot cross, not a measure of success.
Check your understanding
Which sentence is the best engineering problem statement?
A team writes 'the chair should feel comfortable.' Why is this a weak criterion?
'The bridge model must use no more than 50 craft sticks and be built in 30 minutes.' These are:
Recap
An engineer converts a vague complaint into a sharp problem statement naming the user, need, measurable criteria, and constraints in one sentence, where criteria are testable success goals and constraints are limits including scientific principles and real-world impacts.
Reflect
Which constraint do beginners most often forget when they first define a problem?