A line goes on forever both ways. A segment has two ends. A ray has one end and goes on forever the other way.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Some lines never meet.
Parallel lines stay the same distance apart and never meet.
Some lines meet at a square corner.
Perpendicular lines cross at a right angle.
Look around
Railway tracks are parallel. The corner of a page is perpendicular.
Three things that all look straight
A line goes on forever in both directions. A ray starts at a point and goes on forever in one direction. A segment has two endpoints and a definite length. All three are drawn as straight marks, so the arrows and dots at the ends carry the meaning.
Only segments have a length
You can measure a segment because it stops at both ends. A line and a ray have no length to measure. This matters when a question asks for the length of something — it is quietly telling you the object is a segment.
Parallel and perpendicular
Parallel lines stay the same distance apart forever and never meet. Perpendicular lines cross at a right angle. Both describe a relationship between two lines rather than a property of one, which is why they always come up in pairs.
Naming them with letters
Segment AB runs from point A to point B. Ray AB starts at A and passes through B — so ray AB and ray BA are different, while segment AB and segment BA are the same. The order of the letters matters for rays and not for segments.
Step 2: Try It Yourself
Tap and try it out.
90° is a right angle.
Step 3: Watch an Example
One step at a time.
Watch Leo Sort the Lines
Leo is shown three drawings that all look straight.
- Step 1
The first has arrows on both ends, so it is a line.
Step 4: Your Turn
Practice makes it stick.
The Tracks
Problem 1 of 2
Railway tracks never meet. What are they called?
The Corner
Problem 2 of 2
Two lines cross at 90 degrees. What are they called?
Which Is Which?
1 of 4
Which has exactly two end points?
2 of 4
Which has one end point and goes on forever?
3 of 4
At how many degrees do perpendicular lines cross?
4 of 4
Do parallel lines ever meet?
Step 5: Quick Check
Show what you know.
Question 1 of 2
At how many degrees do perpendicular lines cross?
Question 2 of 2
Which goes on forever in both directions?
What You Learned
- A line goes on forever, a segment stops, a ray does one of each.
- Parallel lines never meet.
- Perpendicular lines cross at a right angle.