Segments, Rays, Parallel Lines, and Planes

Lesson Plan - Get It!

Audio:

Vocabulary You can look up all definitions at Mathwords.com. Be sure to write them down and even memorize them!

• segment
• ray
• skew lines
• parallel lines
• parallel planes

This unit has already covered points, lines, and planes, and terms like "collinear" and "coplanar" (Refer to the Points, Lines, and Planes lesson and the Patterns and Inductive Reasoning lesson.)

This lesson continues to introduce you to parts of geometric figures. Specifically, this lesson will introduce you to the vocabulary words listed above.

Before moving any further into the lesson, locate a box you can put on the table in front of you. A picture of a box has been inserted below for reference to the content.

Take a look at the top of your box. The edges are good examples of line segments. Reflect back on the explanation of a line. A line goes on indefinitely in both directions. A line segment, however, has a definite beginning and a definite ending point. As you look at one of the edges on the top of the box, you can see that each edge begins at one corner and ends at another (See the example below):

Now, locate another edge on the top of the box that does not intersect with the line illustrated above (See below):

The two lines illustrated above are known as parallel lines, two lines that do not intersect each other.

Another new term discussed in this lesson is skew lines. They are two lines that do not intersect each other and are not parallel to each other (See below):

As you can see in the illustration above, if both the line segments highlighted on the box were lines, and extended indefinitely in both directions, they would never intersect each other, nor are they parallel.

To conclude the discussion on lines and line segments, you need to be familiar with the term ray. A ray has a definite beginning point, but the end goes on indefinitely (See below):

Take another look at your box, but this time, look at any of the sides, or the top, or the bottom. It's your choice! Each of those flat surfaces is a great example of a plane! Just like lines and line segments, planes can be parallel too! One example of a set of parallel planes is the top and the bottom of the box. Can you find two more sets of parallel planes? Show them to your teacher.

Now you have added to your knowledge of the parts of geometric figures.

The following Got It? section has some activities for you to practice the new terms you just learned.