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Scientific Inquiry and Skills - Evaluating Scientific Evidence and Methods

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Independent Variable (IVIV) is the factor changed by the investigator, while the Dependent Variable (DVDV) is the factor measured in response.

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Controlled variables are kept constant to ensure a 'fair test,' meaning any change in the DVDV is likely due to the IVIV alone.

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Validity refers to whether an experiment actually tests the hypothesis it was designed to test. It is improved by controlling all extraneous variables.

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Reliability (or Repeatability) refers to the consistency of results. It is improved by conducting multiple trials (n≥3n \ge 3) and calculating a mean (ar{x}).

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Accuracy is how close a measurement is to the true or accepted value, whereas Precision is how close repeated measurements are to each other.

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Systematic errors (e.g., a scale not set to zero) affect accuracy consistently in one direction. Random errors (e.g., human reaction time) affect precision and result in data spread.

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An outlier is a data point that differs significantly from other observations; it should be identified and analyzed before deciding whether to exclude it from the mean calculation.

📐Formulae

Mean (xˉ)=∑i=1nxin\text{Mean } (\bar{x}) = \frac{\sum_{i=1}^{n} x_i}{n}

Percentage Error=∣Experimental Value−Theoretical ValueTheoretical Value∣×100%\text{Percentage Error} = \left| \frac{\text{Experimental Value} - \text{Theoretical Value}}{\text{Theoretical Value}} \right| \times 100\%

Range=xmax−xmin\text{Range} = x_{max} - x_{min}

Density (ρ)=mV\text{Density } (\rho) = \frac{m}{V}

💡Examples

Problem 1:

A student measures the boiling point of pure water at sea level three times and records: 98.2∘C98.2 ^\circ C, 98.1∘C98.1 ^\circ C, and 98.3∘C98.3 ^\circ C. If the theoretical boiling point is 100.0∘C100.0 ^\circ C, evaluate the precision and accuracy.

Solution:

The mean is xˉ=98.2+98.1+98.33=98.2∘C\bar{x} = \frac{98.2 + 98.1 + 98.3}{3} = 98.2 ^\circ C. The percentage error is ∣98.2−100.0100.0∣×100=1.8%\left| \frac{98.2 - 100.0}{100.0} \right| \times 100 = 1.8\%.

Explanation:

The results have high precision because the range is small (0.2∘C0.2 ^\circ C), but low accuracy because the values are consistently lower than the 100.0∘C100.0 ^\circ C theoretical value. This suggests a systematic error, possibly an uncalibrated thermometer.

Problem 2:

In an experiment investigating the effect of mass (mm) on the acceleration (aa) of a trolley, a student identifies that the force (FF) must be kept constant. Which variables are which?

Solution:

Independent Variable (IVIV) = Mass (mm); Dependent Variable (DVDV) = Acceleration (aa); Controlled Variable = Force (FF).

Explanation:

The student changes the mass to see how it affects acceleration, making mass the IVIV. The acceleration is the result measured (DVDV). Force is held constant to isolate the relationship between mm and aa (F=maF = ma).

Evaluating Scientific Evidence and Methods Revision - Grade 8 Science IB