IP Combined Science Notes (Lower Sec, Year 1-2): 01) Scientific Inquiry & Measurement

Mastering scientific inquiry starts with disciplined measurement. Every experiment you run — from monitoring temperature change to tracking a plant's growth — demands clear objectives, calibrated tools, and consistent data handling.

Learning targets

• Frame testable scientific questions with defined variables and controls.
• Select appropriate instruments and determine their precision limits.
• Convert between common SI units and express values with correct significant figures.
• Analyse data trends, calculate gradients, and justify conclusions with evidence.

1. Variables & experimental design

Write research questions using the format: "How does \( \text{independent variable} \) affect \( \text{dependent variable} \)?" For example, "How does the concentration of hydrochloric acid affect the rate of magnesium ribbon dissolution?"

2. Measuring instruments & precision

Always state readings as \( \text{value} \pm \text{half smallest division} \) unless otherwise specified.

3. Unit conversions & significant figures

Base SI units

Composite units follow logically: \( \pu{m.s-1} \) for speed, \( \pu{kg.m-3} \) for density, \( \pu{Pa} = \pu{N.m-2} \) for pressure.

Worked example — Density conversion

A stone has mass \( \pu{245 g} \) and volume \( \pu{120 cm3} \).

1. Convert mass: \( \pu{245 g = 0.245 kg} \).
2. Convert volume: \( \pu{120 cm3 = 1.20 \times 10^{-4} m3} \).

\[ \rho = \frac{m}{V} = \frac{0.245}{1.20 \times 10^{-4}} = 2.04 \times 10^{3} \space \pu{kg.m-3}. \]

Use 3 significant figures because the original measurements carry 3 s.f.

4. Graphing & data analysis

• Plot independent variable on the horizontal axis and dependent variable on the vertical axis.
• Include axis labels with units, e.g. \( \text{Temperature/\pu{^\circ C}} \).
• Draw best-fit lines. For linear relationships, calculate gradient using two well-separated points on the line, not raw data pairs.

Gradient calculation

Suppose a heating curve shows temperature rising from \( \pu{22 ^\circ C} \) to \( \pu{58 ^\circ C} \) over \( \pu{180 s} \).

\[ \text{Gradient} = \frac{\Delta T}{\Delta t} = \frac{58 - 22}{180} = 0.20 \space \pu{^\circ C.s-1}. \]

Uncertainty interpretation

If the stopwatch precision is \( \pm \pu{0.01 s} \) and you measure \( \pu{180.32 s} \), state time as \( \pu{(180.32 \pm 0.01) s} \). When calculating gradient, propagate uncertainty qualitatively: discuss how measurement scatter or reaction time could affect slope.

5. Drawing conclusions

Use data trends and scientific reasoning together:

• Evidence: "Temperature rose at \( \pu{0.20 ^\circ C.s-1} \)."
• Explanation: "This shows the heater supplied energy at a nearly constant rate, consistent with the electrical power calculated from \( P = VI \)."
• Evaluation: Mention anomalies, random/systematic errors, and improvements (e.g. repeating trials, calibrating instruments).

Try it yourself

1. State the independent, dependent, and control variables for an investigation into how pH affects enzyme activity.
2. Convert \( \pu{75.0 km.h-1} \) to \( \pu{m.s-1} \) with correct significant figures.
3. A data logger records voltage every \( \pu{0.5 s} \). Plotting current versus voltage gives a straight line passing through \( \pu{(0.35 A, 1.4 V)} \) and \( \pu{(0.90 A, 3.6 V)} \). Calculate the gradient and interpret it.

Continue with matter modelling at https://eclatinstitute.sg/blog/ip-combined-sciences-lower-sec-notes/IP-Combined-Science-Lower-Sec-02-Particle-Model-of-Matter-and-States.