NCERT Book Class 6 Maths Symmetry

Symmetry

13.1 Introduction

Symmetry is quite a common term used in day to day life. When we see certain figures with evenly balanced proportions, we say, “They are symmetrical”. These pictures of architectural marvel are beautiful because of their symmetry.

Suppose we could fold a picture in half such that the left and right halves match exactly then the picture is said to have line symmetry (Fig 13.1). We can see that the two halves are mirror images of each other. If we place a mirror on the fold then the image of one side of the picture will fall exactly on the other side of the picture. When it happens, the fold, which is the mirror line, is a line of symmetry (or an axis of symmetry) for the picture.

The shapes you see here are symmetrical. Why?

When you fold them along the dotted line, one half of the drawing would fit exactly over the other half. 

How do you name the dotted line in the figure?

Where will you place the mirror for having the image exactly over the other half of the picture?

The adjacent figure 13.2 is not symmetrical. Can you tell ‘why not’?

Do This

Take a piece of paper. Fold it in half.

Spill a few drops of ink on one half side.

Now press the halves together.

What do you see?

Is the resulting figure symmetric? If yes, where is the line of symmetry? Is there any other line along which it can be folded to produce two identical parts?

Try more such patterns.

Inked-string patterns

Fold a paper in half. On one half-portion, arrange short lengths of string dipped in a variety of coloured inks or paints. Now press the two halves. Study the figure you obtain. Is it symmetric? In how many ways can it be folded to produce two identical halves?

List a few objects you find in your class room such as the black board, the table, the wall, the textbook, etc. Which of them aresymmetric and which are not? Can you identify the lines of symmetry for those objects which are symmetric?

Please refer to attached file for NCERT Class 6 Maths Symmetry