Engineering and Design

Variables in experiments include the independent variable (what you change), dependent variable (what you measure), and controlled variables (what you keep the same).

Engineers use the design process to solve problems: identify the problem, research, brainstorm solutions, build a prototype, test it, evaluate results, and improve the design.

"Which paper towel is best?" cannot be answered. "Which paper towel soaks up the most water in 30 seconds?" can, because it names what to measure and for how long. Turning a vague question into a testable one is the first move in every investigation.

Each tool measures one quantity to one level of detail. A ruler gives length to the millimetre, a measuring cylinder gives volume, a balance gives mass and a thermometer gives temperature. Using the wrong one gives a number that answers nothing.

When one measurement sits far away from the others, it is an anomaly. Look for a cause — a slipped ruler, a mistimed stopwatch — and repeat that reading. Do not simply cross it out because it spoils a neat pattern.

Engineers test to destruction on purpose. Loading a structure until it fails tells you where the weak point is, which is the only reliable way to know what to strengthen next time.

A design is only good if the person who has to use it can. Testing your build with a real user almost always finds something you never noticed, because you already knew how it was supposed to work.

Most household waste is buried in landfill, where it breaks down slowly or not at all. Sorting waste at the point it is thrown away is what makes recycling possible, because mixed waste is far harder to separate later.