Do I need a lab to practise?

No, the Paper 3 graph and analysis skills can be practised from home with example data.

Which variable goes on which axis?

The manipulated variable, the one you change, goes on the horizontal x-axis, and the responding variable, the one you measure, goes on the vertical y-axis. A derived quantity such as T² is treated as the responding value.

Should I always draw a straight line?

No. Draw a straight best-fit line only if the points genuinely fall along a line. If they follow a bend, draw a smooth curve instead, and never join the points dot to dot.

Why do my scales matter for marks?

A scale based on 1, 2 or 5 that makes the points fill more than half the grid is part of the mark scheme. A cramped plot in one corner loses the scale mark and makes the gradient less accurate.

Science skill: Plotting a good graph, SPM Physics Paper 3

Exam tip

This is a Paper 3 (practical) skill. Practise it from home with example data, no lab needed.

Aim

To learn how to plot a clear, accurate graph that shows the relationship between two variables.

Variables

Manipulated: The manipulated variable is plotted on the horizontal x-axis.
Responding: The responding variable is plotted on the vertical y-axis.
Constant: Constant variables are not plotted; they are stated in the title or notes.

Apparatus & materials

Graph paper
A sharp pencil
A long ruler
The data table

Procedure

Put the manipulated variable on the x-axis and the responding variable on the y-axis, labelling each with the quantity and unit.
Choose simple scales (based on 1, 2 or 5) so that the plotted points fill more than half of the graph paper.
Plot each point accurately with a sharp pencil, using a small cross or a dot in a circle.
Draw a single best-fit line with a ruler (a straight line) or a smooth curve, so the points are balanced on both sides.
Give the graph a title that names the two quantities being plotted.

Tabulating results

Read the values to plot straight from your data table, using the manipulated-variable column for the x-values and the responding-variable (or derived) column for the y-values.

The graph

A well-plotted graph has labelled axes with units, sensible scales, accurately plotted points, and a single best-fit line or smooth curve rather than a dot-to-dot line.

Analysis

Examiners award credit for axes labelled with the correct quantity and unit, for scales on which the points cover more than half the paper, for all points plotted correctly, and for a smooth best-fit line.

Precautions

Avoid awkward scales such as multiples of 3 or 7, which make plotting hard.
Use a sharp pencil so points and lines are thin and precise.
Draw a best-fit line through the trend, not a line joining every point.

Sample results and what they show

Suppose you are plotting the extension of a spring against the load hung on it. A typical set of example readings (not real data) might be: load 1.0 N gives extension 2.0 cm, 2.0 N gives 4.1 cm, 3.0 N gives 5.9 cm, 4.0 N gives 8.2 cm, and 5.0 N gives 10.0 cm.

Reading down the two columns, the extension roughly doubles when the load doubles, so the two quantities rise together in step. That pattern tells you the points will lie close to a straight line, so a ruled best-fit line is the right choice rather than a curve.

The manipulated variable, load in N, goes on the x-axis.
The responding variable, extension in cm, goes on the y-axis.
Each pair of numbers becomes one plotted point, for example (3.0, 5.9).

Deciding the likely shape from the table first stops you forcing a straight line through points that actually curve, or a curve through points that are really straight.

Reading the graph and finding the answer

Plot extension (y-axis) against load (x-axis). Because the readings climb together in step, the points lie along a straight line that passes close to the origin, confirming that extension is directly proportional to load within the elastic limit.

To find the gradient, draw a large triangle on the best-fit line using two points on the line that are far apart, not raw data points. Read their coordinates, for example (1.0 N, 2.0 cm) and (5.0 N, 10.0 cm).

gradient = (10.0 cm − 2.0 cm) ÷ (5.0 N − 1.0 N) = 8.0 cm ÷ 4.0 N = 2.0 cm N⁻¹

The gradient of 2.0 cm N⁻¹ is the extension produced by each newton of load. A larger gradient would mean a softer spring that stretches more easily.

Always write the unit on the gradient, because a bare number carries no marks.

Marks examiners look for

In Paper 3 the graph itself is marked against a checklist, so tidy work earns easy marks.

Label both axes with the quantity and its unit, for example load / N and extension / cm.
Choose scales based on 1, 2 or 5 so the plotted points fill more than half the grid in each direction.
Plot every point accurately with a sharp pencil, using a small cross or an encircled dot.
Draw one thin best-fit line so the points are balanced on both sides, rather than joining dot to dot.

The science-process skills being tested are communicating data clearly and using the space on the grid. Give the graph a title naming the two quantities, keep the pencil sharp so points stay precise, and avoid awkward scales such as multiples of 3 or 7 that make reading values difficult.

A neat line through the trend shows you can interpret the relationship, not just record it.

Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)

Written by the spmphysics.com.my editorial team.· Updated 5 Sept 2026

Science skill: Plotting a good graph

Aim