Lab Skills
9th Grade Science · 8 lessons
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Lessons in this unit
- 1Variables: Independent, Dependent and ControlThe independent variable is the one you deliberately change, the dependent variable is what you measure, and control variables are everything you deliberately hold constant. Change two things at once and no conclusion about cause is available.Lesson
- 2Accuracy, Precision and ResolutionAccuracy is closeness to the true value; precision is how tightly repeated readings cluster. They are independent — a badly zeroed balance can be very precise and consistently wrong. Resolution is the smallest change an instrument can show.Experiment
- 3Systematic and Random ErrorsA systematic error shifts every reading the same way — a zero offset or a mis-calibrated scale — and repeating does not help; only correcting the instrument does. Random error scatters readings both ways, and taking a mean of repeats reduces it.Experiment
- 4Uncertainty and Significant FiguresEvery measurement carries an uncertainty, usually half the smallest scale division or the spread of repeats. A calculated answer can never be more precise than its least precise input, so quote results to the same number of significant figures as your weakest measurement.Experiment
- 5Anomalies, Repeats and the MeanAn anomalous result sits well outside the pattern of the others. Identify it, look for a cause, and exclude it from the mean only with that reason recorded. Never delete a point simply because it spoils an expected trend.Lesson
- 6Graphs: Lines of Best Fit and GradientsPlot the independent variable on the x-axis and the dependent on the y-axis, scale both to fill the grid, and draw a single smooth line of best fit rather than joining dots. The gradient often is the physical quantity you actually wanted.Lesson
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