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Pure · Vectors

Chapter 1 · 4

The idea

Vector notation and representation

What a vector is (a size and a direction), the ways we write one (bold letter, arrow, column, i–j components), and how to add, subtract and scale vectors — both geometrically (nose-to-tail) and component by component.

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Pure · Vectors

Vector notation and representation

What a vector is (a size and a direction), the ways we write one (bold letter, arrow, column, i–j components), and how to add, subtract and scale vectors — both geometrically (nose-to-tail) and component by component.

Why it works

A size and a direction

A scalar is just a size — 55, −3-3, a temperature. A vector carries a size and a direction: a displacement of "55 km north-east", a velocity, a force. We draw one as an arrow (a directed line segment): its length is the magnitude and the way it points is the direction.

Four ways to write one

  • a bold letter a\mathbf{a} (handwritten: underlined, a‾\underline{a});
  • an arrow between two points, AB⃗\vec{AB} — "from AA to BB";
  • a column, (xy)\begin{pmatrix} x \\ y \end{pmatrix};
  • in terms of the unit vectors i\mathbf{i} (one unit along the xx-axis) and j\mathbf{j} (one unit along the yy-axis): xi+yjx\mathbf{i} + y\mathbf{j}.

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