Scientific reading
Engineering means meeting a defined requirement
A proposed energy-conversion device must provide a minimum useful output within a deadline while respecting an input-energy budget. These requirements involve three separate quantities: E_useful, elapsed time and E_input. Feasibility cannot be determined by efficiency alone, and a fast but wasteful device can be unacceptable under an energy-budget constraint.
Three numerical constraints
Consider a class design brief: no more than 500 J of input, at least 300 J of useful output, and at most 6 seconds elapsed. A design with E_in=400 J, η=75% and t=5 s meets all three requirements, because E_useful=300 J. A design with 400 J, η=60%, 5 s fails useful output, despite using the same input and time.
Power–efficiency trade-offs
A device can achieve greater useful power by reducing the time or increasing useful energy. Its efficiency improves only if the useful fraction of input rises. Other design criteria—reliability, lifetime, accessibility, environment, cost and safety—remain outside this small energy-only optimization. The lab is a numerical design challenge, not an invitation to wire a motor or test appliances.
Make reproducible evidence
State the constraints and a hypothesis. Hold two variables fixed while changing one, then record three comparable runs. Export your notebook or use CSV samples. Explain why a design passes or fails and name a missing engineering constraint that the model cannot assess.