Every Good Design Starts With Clear Requirements
Atlas stands at a wooden workbench covered with sketches, rulers, and colored sticky notes, holding up a handwritten list titled 'What My Bridge Must Do' while pointing excitedly at each item.
- Explain what a design requirement is in your own words.
- Identify the difference between what a design must do (criteria) and the limits it must stay within (constraints).
- Predict what might go wrong when an engineer skips writing requirements before building.
- Give one example of a criterion and one example of a constraint for a project you know.
Key terms
- requirement
- a rule your design must follow
- criteria
- the jobs your design must do
- constraint
- a limit you cannot break
- target
- the goal you aim for
Criteria: The Jobs
Criteria are the jobs your design must do well. They tell you what success looks like. For a bridge, a criterion might be that it must hold a toy car as heavy as a small apple. Another criterion might be that a toy car can drive across it. Criteria are about what the finished thing must achieve. If your design does the jobs on your criteria list, you have a winner.
Constraints: The Limits
Constraints are the limits you have to stay inside. They are rules you cannot break. A constraint might say you can only use craft sticks and glue. Another might say you must finish in one class. Constraints control your materials, your time, and your money. They do not say what to build. They say what you are allowed to use while you build it.
Worked examples
Is 'the backpack must hold 5 kg of books' a criterion or a constraint?
- Ask what the backpack must DO.
- Holding 5 kg is a job, not a limit.
Answer: It is a criterion, because it is a job the design must do.
Is 'you may only use newspaper and tape' a criterion or a constraint?
- Ask if this limits your materials.
- It limits what you can use.
Answer: It is a constraint, because it limits your materials.
Activity
Sort each card into the correct bin: is it a Criteria card (what the design must DO) or a Constraints card (a limit on materials, time, or cost that the designer must stay within)?
Practice
Decide if 'the tower must stand on its own' is criteria or constraint.
Write one criterion and one constraint for a paper hat.
Common mistakes to avoid
- Any number is a constraintNumbers can appear in both criteria and constraints.
- Kids do not need requirementsEvery builder needs requirements to know the target first.
Check your understanding
An engineer is designing a backpack for third-graders. She writes: 'The backpack must hold 5 kg of books.' What kind of requirement is this?
A team skips writing requirements and jumps straight into building a model car. What is the most likely problem they will face?
Which of the following is a constraint on a school project?
Recap
Requirements are the rules your design must follow. Criteria are the jobs your design must do. Constraints are the limits you cannot break, like materials or time. Writing both first gives you a clear target before you build.
Reflect
What is one limit you would set for your next build?