ICAS Science cheat sheet

Observations are either qualitative (descriptive, no number) or quantitative (a number with a unit).

Read liquid volume at the bottom of the meniscus with the eye level with the mark to avoid parallax error.

The uncertainty of a single scale reading is about plus or minus half the smallest division of the scale.

Accuracy is closeness to the true value; precision is closeness of repeated readings to one another.

Mean of repeated readings = sum of readings divided by the number of readings; faulty readings are discarded before averaging.

SI base units: metre (length), kilogram (mass), second (time), kelvin (temperature); volume is measured in litres or cubic centimetres.

Conversions: 1 m = 100 cm = 1000 mm; 1 kg = 1000 g; 1 L = 1000 mL; 1 cm3 = 1 mL.

Mass (kg) is the amount of matter and is unchanged by location; weight (N) = mass x gravitational field strength and depends on gravity.

Choose an instrument whose range covers the expected value and whose smallest division matches the precision needed.

On a graph the independent variable is plotted on the x-axis and the dependent variable on the y-axis.

Gradient (slope) = change in y divided by change in x; its units are y-units per x-unit and it represents a rate.

A horizontal line means no change in y as x increases; a downward slope means y decreases as x increases.

Use a line graph for continuous data and a bar chart for data in separate categories.

Interpolate within the plotted range; values read outside the plotted range are less reliable.

Anomalous points that sit off the trend are rechecked and excluded when drawing a line of best fit.

Check axis scales: if the y-axis does not start at zero, small differences can look large.

Correlation between two variables is not evidence that one variable causes the other.

A hypothesis is a testable statement about the relationship between variables; a prediction is the expected result in a specific case.

A conclusion must refer back to the hypothesis and be supported only by the evidence collected.

Extrapolation, predicting beyond the measured range, is less reliable than interpolation within it.

An effect can be attributed to the independent variable only if a control group or controlled conditions are used.

If results do not match the prediction, check the method and repeats before revising the hypothesis.

Larger samples and repeated trials increase confidence in a conclusion.

State results with units and compare values numerically rather than describing one as simply 'bigger'.

Trend types: proportional (straight line through the origin), linear (straight line with an intercept) or non-linear (curve).

Fair test: change the independent variable, measure the dependent variable, and keep all controlled variables constant.

Include a control group that does not receive the treatment, to provide a baseline for comparison.

Reliability is improved by repeating trials and averaging; validity requires the method to measure what it claims to measure.

Random sampling reduces bias; a larger sample is more representative of the population.

Record data in a table whose headings give the variable name and its unit.

Choose equipment by range and precision: measuring cylinder for volume, electronic balance for mass to 0.01 g, thermometer for temperature.

Before starting, identify hazards, assess risk and apply controls such as safety goggles, tied-back hair and never tasting chemicals.

In drug trials the control group receives a placebo and, where possible, subjects are randomly assigned to groups.

Check that all quantities are in consistent units before substituting them into a formula.

Key formulas: density = mass / volume; speed = distance / time; force = mass x acceleration.

Percentage change = (new value - old value) / old value x 100%.

Estimate the answer to one significant figure first and compare it with the calculated result to catch errors.

If every length is scaled by a factor k, areas scale by k squared and volumes by k cubed.

As an object gets larger its surface-area-to-volume ratio decreases, affecting heat loss and diffusion rates.

Use proportional reasoning: if a corresponds to b, then n x a corresponds to n x b; set up a ratio and solve for the unknown.

Separate evidence from assumption by stating what the data show and what is being inferred.

Eliminate implausible options by checking units, direction of change and order of magnitude.