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blade length
The other stated conditions are kept comparable.
Class 7 · Bangla Version · General science
Scientific investigation and evidence
Design a fair comparison and judge the strength of its conclusion.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
Change one explanatory factor where practical, measure the outcome and keep relevant conditions comparable. Repeat measurements to assess consistency. Random assignment can reduce systematic differences between groups. A small difference with noisy measurements may not support a firm conclusion.
Worked example
To compare paper helicopter designs, keep paper type and release height the same, vary blade length and measure fall time repeatedly. A single lucky drop cannot identify the better design.
- State a testable question.
- Plan variables, repeats and safe measurement.
- Compare results and explain uncertainty.
Stretch example
A reading of 12.0 ± 0.2 cm expresses a stated measurement uncertainty of 0.2 cm on either side, under the method used. It is not a guarantee that every possible error is within that interval.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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3
9 divided by 3 gives 3 seconds.
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no
Investigate and report the reason for any exclusion.
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Repeats show whether differences are consistent rather than just one unusual release.
Explain what repeats reveal.
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The measurements do not show a clear difference under these conditions; more precise repeated work may help.
Avoid claiming equal performance has been proved.
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12.2
12.0 + 0.2 = 12.2.
Write in your own words. A guardian or teacher should review this response.
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A consistently incorrect scale can shift every repeat in the same direction.
Distinguish consistent repetition from accuracy.
Safe investigation plan
Plan a paper-helicopter comparison without using stairs or high places.
Review with a guardian or teacher
- State changed, measured and controlled variables.
- Use a low safe release height.
- Plan repeats and a cautious conclusion.
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