AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
(HT only) Students should be able to use vector diagrams to illustrate…
Full specification wording
Resultant forces: (HT only) Students should be able to use vector diagrams to illustrate resolution of forces, equilibrium situations and determine the resultant of two forces, to include both magnitude and direction (scale drawings only).
Higher tier only, and scale drawings only: no trigonometry is required.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 7 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Higher tier only, and scale drawings only: no trigonometry is required. To find the resultant of two forces, state a scale such as 1 cm represents 20 N, draw the first force to length and direction, then draw the second starting from the tip of the first, keeping its own direction. The resultant runs from the tail of the first arrow to the tip of the second; measure it, convert with the scale, and measure its angle from a stated direction. For equilibrium, three forces acting on an object with a zero resultant form a closed triangle when drawn tip to tail, so if the drawing does not close, the forces are not balanced. Resolution is the same construction used in reverse.
What earns the marks
- A stated scale, such as 1 cm represents 20 N.
- The two forces drawn tip to tail, each to the correct length and direction.
- The resultant drawn from the tail of the first force to the tip of the second.
- Measuring the resultant and converting it to newtons using the stated scale.
- The direction of the resultant given as an angle from a stated reference direction.
Common mistakes and how to put them right
Using Pythagoras or trigonometry when the question specifies a scale drawing.
Drawing the two forces from the same point and joining the tips as if that were the resultant.
Forgetting to write the scale on the diagram.
Quoting the answer in centimetres instead of newtons.
Giving only the magnitude when the question asks for magnitude and direction.
Exam tips
- Choose a scale that uses most of the graph paper, since a bigger drawing gives a smaller percentage error.
- For an equilibrium question, check whether your triangle closes; a gap means you have made a drawing error or the forces are unbalanced.
- Leave the construction lines on the page, because the method marks come from the drawing itself.
Try the lesson
The start of the Resultant forces: (HT only) Students should be able to use vector diagrams to illustrate resolution of forces, equilibrium situations and determine the resultant of two forces, to include both magnitude and direction (scale drawings only). lesson, made from checked teaching notes for this specification point.
Have a go first
A force of 30 N acts horizontally to the right on a box. A second force of 40 N acts vertically upwards on the same box. Using a scale drawing, what is the magnitude of the resultant force on the box?
Listen
Higher tier only, and scale drawings only: no trigonometry is required. To find the resultant of two forces, state a scale such as 1 cm represents 20 N, draw the first force to length and direction, then draw the second starting from the tip of the first, keeping its own direction. The resultant runs from the tail of the first arrow to the tip of the second; measure it, convert with the scale, and measure its angle from a stated direction. For equilibrium, three forces acting on an object with a zero resultant form a closed triangle when drawn tip to tail, so if the drawing does not close, the forces are not balanced. Resolution is the same construction used in reverse. A strong answer earns marks for these points. a stated scale, such as 1 cm represents 20 N. the two forces drawn tip to tail, each to the correct length and direction. the resultant drawn from the tail of the first force to the tip of the second. measuring the resultant and converting it to newtons using the stated scale. Exam tip: Choose a scale that uses most of the graph paper, since a bigger drawing gives a smaller percentage error.
Key words
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scale vector diagrams
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tip to tail construction
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resultant of two forces
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equilibrium and closed triangles
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See every definition
- scale vector diagrams
- Drawings in which a stated scale, such as 1 cm represents 20 N, is used to show forces to length and direction.
- tip to tail construction
- Drawing the first force to length and direction, then drawing the second starting from the tip of the first, keeping its own direction.
- resultant of two forces
- The single force drawn from the tail of the first arrow to the tip of the second, measured and converted with the scale, with its direction given as an angle from a stated direction.
- equilibrium and closed triangles
- Three forces acting on an object with a zero resultant form a closed triangle when drawn tip to tail, so if the drawing does not close the forces are not balanced.
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