Practical requirements
Reliable measurement, data analysis and the investigations in mechanics, thermal transfer, light and resistance.
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Before you begin
The practical paper tests whether you can plan an experiment, take careful readings, draw a good graph and judge what the results show. Physics shares the paper with your other science. The lessons start with the skills every investigation needs: measuring and recording, graphs and evaluating a method. They then work through the investigations for mechanics, heat, light and electricity, from density and free fall to moments, refraction and resistance. Each one prepares the method and the analysis; the readings themselves need supervised laboratory time.
Be comfortable with: physical quantities and units, because every reading needs the right unit, and plotting motion graphs.
Learning goals
- Measurements of length, mass, temperature, time interval, volume of liquids/solids and force (e.g. weight) using appropriate instruments
- Determination of the density of a liquid, or of a regularly or irregularly shaped solid that sinks in water
- Determination of the value of the acceleration of free fall
Syllabus statements covered
- Measurements of length, time interval, volume, mass and weight, temperature, current and voltage using the listed instruments
- Determination of the density of a liquid, or a regularly or irregularly shaped solid, that sinks in water
- Determination of the value of acceleration of free fall
- Investigation of the effects of balanced and unbalanced forces
- The principle of moments
- Determination of the position of the centre of gravity of a plane lamina
- Investigation of the factors affecting transfer of energy by thermal processes
- The law of reflection
- Determination of the position and characteristics of an optical image formed by a plane mirror or a thin converging lens
- The refraction of light through glass blocks
- Determination of the resistance of a circuit component
Lessons
Work through them in order.
- Measuring and recording practical dataChoose instruments, avoid reading errors, time complete oscillations and investigate repeats before recording valid data.
- Graphs and data analysisProcess pendulum readings, draw a best-fit line, use a large gradient triangle and judge what the graph supports.
- Evaluating investigationsLink limitations to effects and improvements, then suggest a modification or, for G3 Science, an extension.
- Density investigationsChoose volume methods for liquids and solids, calculate density from matching mass and volume readings, and explain measurement errors.
- Free-fall investigationEstimate g from an electronic-timing graph and evaluate the distance, release and timing assumptions.
- Balanced and unbalanced forces investigationTest steady motion, keep the total moving mass fixed in a trolley–hanger experiment and interpret acceleration and friction evidence.
- Moments investigationTest the principle of moments with a balanced metre rule, include the rule's own weight and evaluate the balance readings.
- Centre-of-gravity investigationLocate the centre of gravity of a plane lamina with a plumb line, compare traces from different suspension points and evaluate their spread.
- Thermal transfer investigationPlan a fair cooling comparison, draw and compare cooling curves, and evaluate how well the variables were controlled.
- Reflection investigationTrace rays with optical pins, measure angles from the normal and evaluate evidence for the law of reflection.
- Mirror and lens image investigationsLocate a plane-mirror image by removing parallax, find a sharp lens image on a screen and describe observed image characteristics.
- Refraction investigationTrace rays through a glass block, compare sine ratios and use a graph to estimate refractive index with realistic measurement limits.
- Resistance of a componentConnect the meters, record paired readings, interpret a resistance graph and control heating and reading errors.
- Wire length and resistanceMove a wire contact, measure between the contacts, control heating and use ratios and a graph to test the length relationship.
Practise and check
Topic reference
Quick reference
| Skill | What to do |
|---|---|
| choosing an instrument | pick one with a suitable range and the finest useful scale; check its zero first |
| reading a scale | look straight at it to avoid parallax |
| repeating readings | repeat, look for anomalies and take the mean of the consistent values |
| recording | table headings show quantity / unit; values have consistent decimal places |
| graphs | label both axes with quantity / unit, use most of the grid and draw a best-fit line |
| gradient | use a large triangle on the best-fit line, not two data points |
| evaluating | name a limitation, say how it affects the result, then give a matching improvement |
Core knowledge to remember
- In a fair test, change one independent variable, measure the dependent variable and keep the other variables constant.
- Repeat readings to reduce the effect of random errors. A systematic error, such as a zero error, is not reduced by repeating.
- Measure angles in light experiments from the normal.
- A conclusion must be supported by the data, and stated within the range tested.
- An extension investigates a new variable; a modification improves the same experiment.
Common mistakes
- Recording readings without units, or to different numbers of decimal places.
- Ignoring a zero error, or trying to remove a systematic error by repeating readings.
- Calculating a gradient from two data points instead of a large triangle on the best-fit line.
- Giving a vague improvement, such as “be more careful”, instead of one that fixes a named limitation.
- Measuring angles from the mirror or block surface instead of from the normal.