1Parallel means "never meeting"
If two lines never meet at any point, no matter how far you extend them, those lines are parallel. Since the gap between them stays exactly the same from start to finish, there's simply no way for them to meet.
2Perpendicular means "meeting at a right angle"
When the angle formed where two lines meet is exactly 90° (a right angle), the two lines are called perpendicular. Unlike parallel lines, perpendicular lines really do meet at a point — it's just that they meet in a perfectly square way.
On the activity page, set the slider to exactly 90° and watch the shape formed by the two lines change dramatically.
3Any other case is just called "meeting"
If the angle isn't 90° and the lines aren't parallel, there's no special name for it — we just say "the two lines meet." Only two relationships between lines get a special name: parallel and perpendicular.
4The only thing that matters is the "angle"
The only thing that decides the relationship between two lines is the angle where they meet. An angle of 0° (or 180°) means parallel, 90° means perpendicular, and anything in between is just "meeting."
The horizontal and vertical lines of a book, the rungs and side rails of a ladder, a traffic light pole and the road — they're all either parallel or perpendicular.
5Try playing like this
- Move the slider very slowly. Watch exactly when the relationship label changes as the angle gets close to 90° and moves away from it.
- Try to make the lines parallel. Find the angle where the two lines never meet.
- Try the relationship-guessing quiz. Practice telling parallel, perpendicular, and "other" apart just by looking at the angle.