Vectors cannot be added like ordinary numbers unless they act along the same line
Scalars & Vectors - OCR A-Level Physics
- Vectors cannot be added like ordinary numbers unless they act along the same line.
- To add two vectors that act at an angle, use the triangle of vectorsA method for adding two vectors: draw them head-to-tail and the resultant is the third side of the triangle. method.
- Draw the first vector arrow to scale.
- From the tip of the first arrow, draw the second vector arrow to scale.
- The resultantThe single vector that has the same effect as two or more vectors acting together. is the arrow drawn from the start of the first vector to the tip of the second.
- The magnitude and direction of the resultant can be found by measurement (scale drawing) or by calculation (cosine rule, sine rule).
Examiner Tips and Tricks
- In a scale drawing question, always state your scale (e.g. '1 cm represents 5 N'), use a sharp pencil, and a protractor.
- Measure the resultant length and convert back using your scale.
- Examiners expect the answer to be within +/- 5% of the calculated value.
Common Mistake
MEDIUM
Wrong: Drawing both vectors from the same point when using the triangle method.
Right: In the triangle method, vectors are drawn nose-to-tail. The second vector starts at the tip of the first. Drawing them from the same origin is the parallelogram method, not the triangle method.
Right: In the triangle method, vectors are drawn nose-to-tail. The second vector starts at the tip of the first. Drawing them from the same origin is the parallelogram method, not the triangle method.