The scientific method
Introduced| English | Meaning |
|---|---|
| hypothesis/haɪˈpɒθəsɪs/ | A proposed explanation or prediction that can be tested using evidence. |
| independent variable/ˌɪndɪˈpendənt ˈveərɪəbl/ | An input or factor whose value is chosen or varied to examine its effect on another quantity. |
| dependent variable/dɪˈpendənt ˈveərɪəbl/ | The measured or calculated outcome whose response to changes in another variable is studied. |
| control variables/kənˈtrəʊl ˈveərɪəblz/ | Factors kept the same in an investigation so that the effect of the independent variable can be assessed. |
| repeats/rɪˈpiːts/ | Additional measurements made under the same conditions to assess variation and improve confidence in a result. |
| control group/kənˈtrəʊl ɡruːp/ | A comparison group that does not receive the treatment being investigated, or receives a standard alternative. |
Which paper retains more water?
- A class compares equal-sized pieces of paper A and B using the same immersion and draining procedure. It measures retained-water mass, not cleaning strength or value for money.
- A hypothesis 假设 predicts that B's mean retained-water mass will exceed A's under these conditions. Results at or below A's would challenge that prediction.
Which is a testable hypothesis?
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The growth statement can be tested against a defined comparison and conditions. A useful hypothesis needs measurable variables and observations that could challenge it.
Name the change, response and controls
- The independent variable 自变量 is paper type. The dependent variable 因变量 is retained-water mass. Control variables 控制变量 include square area, immersion time and the draining procedure.
- Keep these conditions comparable across A and B. Squeezing only A changes the procedure as well as the paper, so a difference cannot be assigned to paper type alone.
In a hypothetical fertiliser comparison with height measured after four weeks and soil, water and light held comparable, match each element to its role.
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The changed factor, measured response and comparable conditions are distinct. Naming them supports planning but does not guarantee a mark or establish a result.
In a simple comparison intended to isolate fertiliser effects, changing light alongside fertiliser gives the same information as keeping light comparable.
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The paired change cannot isolate fertiliser in that simple comparison. A different, deliberately structured design could investigate multiple factors; do not treat all multi-factor research as impossible.
Name one control variable for an experiment on how temperature affects how fast sugar dissolves.
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Example: "The same mass of sugar with the same grain size in every trial."
Measure the defined response
- For each piece, subtract dry mass from mass after draining: $m_{\text{retained}}=m_{\text{after}}-m_{\text{dry}}$. A heavier wet piece alone need not have retained more water if its dry mass was also larger.
- Use a suitable balance and the same timing and draining method. Record each trial and any observed procedural fault before summarising the results.
A supplied piece has dry mass 1.8 g and mass after draining 4.8 g. Its retained-water mass is $m_{\text{retained}}=4.8-1.8=3.0\ \text{g}$. The subtraction defines the response; it is not an uncertainty estimate.
Dry paper mass is 1.8 g and mass after draining is 4.8 g. What retained-water mass does the defined subtraction give, in g?
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Retained mass = 4.8 - 1.8 = 3.0 g.
Compare the repeat readings
- Invented A readings are 2.8, 3.0 and 3.2 g; B readings are 3.9, 4.2 and 4.5 g. Their means are 3.0 and 4.2 g, a mean difference of 1.2 g in this record.
- Repeats 重复测量 show variation: A ranges from 2.8 to 3.2 g and B from 3.9 to 4.5 g. Repeating an unequal procedure does not fix it; three trials and separate ranges are not a complete statistical test.
From A readings 2.8, 3.0, 3.2 g and B readings 3.9, 4.2, 4.5 g, how much larger is B's mean, in g?
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A mean is 3.0 g; B mean is 4.2 g. The difference is 1.2 g.
Use a comparison that answers the question
- A control group 对照组 gives a no-treatment comparison where needed. In a fertiliser study, plants without fertiliser can show growth without that treatment; soil, water and light still need comparable conditions.
- A and B already provide the paper-type comparison. An unused dry piece is useful for some checks, but does not replace comparing retained-water measurements from both paper types.
Why include plants that get no fertiliser at all?
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A no-fertiliser comparison helps separate growth under the treatment from growth without it, subject to the rest of the design. It does not remove every possible confound.
Report the finding and the limits
- B's observed mean exceeds A's by 1.2 g under this procedure. The result supports the stated prediction for the tested pieces; it does not establish every batch, cleaning performance, cost or strength.
- Keep unexpected results and explain any evidence-based exclusion. Follow the teacher's approved procedure for practical work; this invented dataset is for analysis.
Define the response, keep the comparison fair, retain trial readings, then give a conclusion whose scope matches the data. Planning and results may lead you to revise the method or question.
Repeating a comparison many times fixes the fault of squeezing only paper A.
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False: the unequal draining procedure remains unequal across repeats.