Science: research summaries, controls and engineering tests
| English | Português |
|---|---|
| controlled variable/kənˈtrəʊld ˈveərɪəbl/ | controlled variable |
| constraint/kənˈstreɪnt/ | constraint |
A decision before an answer
- Changing two design features at once may reveal a better device, but it cannot identify which feature caused the improvement.
- Your goal: Identify independent, dependent and controlled variables across experiments.
Read the relationship
- Research Summaries passages describe experiments with related but distinct designs. Make a compact table of what changed, what was measured and what stayed fixed. Compare experiment numbers carefully: the same material might be used at a different volume, temperature or duration. A control supplies a comparison for a stated effect; it is not necessarily a trial with no treatment in every possible experiment.
- Choose a follow-up that isolates the proposed explanation.
Which design satisfies cost ≤5 and deflection ≤4 mm?
A satisfies both inequalities; B exceeds cost.
Use the defining rule
- To isolate a variable, hold relevant alternatives constant and vary that variable deliberately. Repeated trials assess variability and reduce reliance on one observation. Random allocation can reduce systematic group differences when the design permits it. A result from one apparatus, duration or population does not automatically generalise to another.
- Apply engineering criteria and constraints to a design comparison.
To isolate thickness, which should stay fixed?
Alternative causal conditions must be controlled while thickness changes.
Check the conditions
- A follow-up experiment should distinguish the proposed explanations. Predict what each would expect and choose a measurement capable of separating them. Extending a study to a new range tests generality, but changing several conditions simultaneously can prevent a causal interpretation. State whether the new task explores a relationship or isolates an explanation.
- Apply engineering criteria and constraints to a design comparison.
Original engineering study: beams A and B are tested at a 10 N load with identical length and supports. A costs 4 units and deflects 3 mm; B costs 7 and deflects 1 mm. Required cost ≤5 and deflection ≤4 mm. A satisfies both constraints; B fails cost despite smaller deflection. To test whether thickness explains deflection, use beams of the same material, length and support geometry at several thicknesses under the same load. Testing one thick wooden beam and one thin metal beam confounds material with thickness. Repeated measurements can reveal variation, but repetition alone does not remove that confounding.
The measured beam deflection is the ____ variable: independent or dependent?
Deflection is the measured response to changes or a test load.
Apply the task format
- Engineering tasks add a goal, measurable criteria and constraints such as cost, mass or allowable deflection. A design is acceptable only when it satisfies the required constraints. Optimising one measurement does not necessarily make it best overall. A fair comparison applies the same test load and procedure, with repeat trials where feasible.
- Apply engineering criteria and constraints to a design comparison.
A repeated confounded experiment remains confounded. Best performance on one metric can fail the design brief.
Which answer fits this case?
Identify independent, dependent and controlled variables across experiments
Repeating a test automatically removes a confounding variable.
It measures variability but does not untangle systematically linked changes.
Keep the distinctions
- controlled variable 控制变量 — A relevant condition held fixed to support a fair comparison.
- constraint 约束条件 — A required limit that an acceptable design must satisfy.
- Identify independent, dependent and controlled variables across experiments.
- Choose a follow-up that isolates the proposed explanation.
- Apply engineering criteria and constraints to a design comparison.
Match each term with its precise meaning in this lesson.
Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
The order follows the stated process; check each stage before the next.