Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Use vector diagrams to illustrate resolution of forces, a net force, and…
Full specification wording
Topic 9 – Forces and their effects: 9.3 Use vector diagrams to illustrate resolution of forces, a net force, and equilibrium situations (scale drawings only)
Vector diagrams show forces as arrows whose length represents magnitude on a chosen scale and whose direction shows the line of action.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 3 of 9
Study notes
From the checked teaching notes for this specification point.
The idea
Vector diagrams show forces as arrows whose length represents magnitude on a chosen scale and whose direction shows the line of action. To resolve a force, draw it to scale and construct a rectangle from perpendicular components, then measure each side and convert using the scale. To find a net force, place the force arrows tip to tail and draw the resultant from the start of the first arrow to the tip of the last. An equilibrium situation is shown when the vector triangle or polygon closes, so the resultant is zero. Worked method: choose a scale such as 1 cm = 10 N, draw accurately with a ruler and protractor, measure the unknown length, then multiply by the scale factor. Only scale drawings are required, so answers come from measurement and conversion rather than trigonometry.
What earns the marks
- Selects a stated scale and draws each force arrow with a length proportional to its magnitude.
- Constructs a rectangle or parallelogram to resolve a single force into two perpendicular components.
- Measures the drawn resultant and converts its length using the chosen scale to give the net force.
- Identifies equilibrium when the vector diagram closes so the resultant force is zero.
- Places arrows tip to tail in the correct order when combining two or more forces.
Common mistakes and how to put them right
Draws arrows without a stated scale.
Put it right: State the scale and keep every arrow consistent with it.
Adds magnitudes arithmetically for forces at an angle.
Put it right: Construct the vector diagram and measure the resultant instead.
Treats a closed vector triangle as showing a large net force.
Put it right: Recognise that a closed diagram means the resultant is zero.
Measures the component but forgets to convert using the scale.
Put it right: Multiply the measured length by the scale factor.
Exam tips
- Write the scale at the top of the diagram before drawing any arrow so the examiner can follow your conversion.
- Use a sharp pencil, ruler and protractor, and measure to the nearest millimetre for accuracy.
- State the direction of the resultant as well as its magnitude, for example an angle from a named reference line.
Try the lesson
The start of the Topic 9 – Forces and their effects: 9.3 Use vector diagrams to illustrate resolution of forces, a net force, and equilibrium situations (scale drawings only) lesson, made from checked teaching notes for this specification point.
Have a go first
On a scale drawing, a single force arrow is replaced by two arrows drawn at right angles that together have the same effect. What is this process called?
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