Draw a dot on paper. Now draw another dot. Can you join them with a straight mark? That mark is a line segment! Lines are the building blocks of all shapes. In this chapter we learn about straight lines, curved lines, and how lines can be arranged around us.
What will we learn?
We will identify straight lines and curved lines, understand horizontal, vertical, and slanting lines, and explore how lines make patterns and shapes.
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Key Concepts
Straight line: Goes in one direction without bending.
Curved line: Bends or turns — like a smile or a wave.
Horizontal line: Goes across (left to right), like the horizon or a sleeping line. (----)
Vertical line: Goes up and down (standing straight), like a flag pole. (|)
Slanting (diagonal) line: Goes at an angle, like a slide. (/)
Line segment: A part of a line with two endpoints. The sides of shapes are line segments.
Open and closed figures: A closed figure is when lines join up to form a complete shape (like a triangle). An open figure is when lines do not join up completely.
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Worked Examples
Is the line across the top of a table horizontal or vertical?
The top of a table goes across — it is a horizontal line.
Name two things in your classroom that show a vertical line.
A door frame and a flagpole are examples of vertical lines.
How many straight line segments does a triangle have?
A triangle has 3 straight line segments as its sides.
A child draws a shape that is fully closed with 4 straight lines. Is it open or closed? How many sides?
It is a closed figure with 4 sides (a quadrilateral like a square or rectangle).
Is a river on a map an example of a straight line or a curved line?
A river bends and turns — it is a curved line.
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Common mistakes
- A line segment has a start and an end point. A full line goes on forever in both directions — we usually draw line segments in class.
- Students sometimes call diagonal lines "broken" — slanting lines are straight, just at an angle.
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Summary
Lines can be straight or curved. Straight lines can be horizontal, vertical, or slanting. When line segments join to make a closed shape, we get figures like triangles, squares, and rectangles. Lines are the first step in drawing any shape!