A stretched thread, the path of an ant, the outline of a cloud: these are all lines. Some are straight, others curve.

Straight and curved, open and closed

  • A straight line does not change direction, like a tightly stretched string.
  • A curved line changes direction all the time, like the path of a snake.
  • A closed line ends where it began, like the outline of a circle.
  • An open line has two loose ends.

A line made only of straight pieces is a polygonal. When it is closed, it draws a polygon.

What kind of line is this? Click on the answer and try five hits in a row.

Parallel and perpendicular lines

Think of train tracks: they run side by side and never meet. Lines like this are parallel.

Now think of a corner where two streets intersect forming a “sheet of paper corner”. These straight they are perpendicular: they intersect forming four right angles.

Lines that intersect without forming straight corners are called concurrent.

Drag the balls to move the straight lines and find out when they are parallel, concurrent or perpendicular.

ResumoWhere to find

  • Parallels: train tracks, notebook lines, street lanes, guitar strings.
  • Perpendiculars: corners of doors and windows, intersection of grid lines, the letter T.
  • Competitors: the hands of an open scissors, the letter X.
Check the answer

Parallels: E (the three lines lying down), H (the two standing up), N (the two standing up) and Z (the two lying down). Perpendiculars: E, H, L and T. The V only has competing lines, which form an acute angle.

True or false?

  1. The outline of a coin is a closed curved line.
  2. Parallel lines intersect very far away.
  3. The sides of a notebook page that meet at the corner are perpendicular.
  4. Every line that intersects another is perpendicular to it.