Short Notes: Understanding Elementary Shapes

# Understanding Elementary Shapes Class 6 Notes Maths Chapter 5

 Table of contents Measuring Line Segments Angles – “Right” and “Straight” Acute, Obtuse and Reflex Angles Measuring Angles Perpendicular Lines Perpendicular Bisector Classification of Triangles Quadrilaterals Polygons

There are so many shapes around us made up of lines and curves like line segments, angles, triangles, polygons and circles etc. These shapes are of different sizes and measures.

## Measuring Line Segments

A line segment is a fixed part of the line, so it must have some length. We can compare any line segment on the basis of their length.

1. Comparison by Observation
We can tell which line segment is greater than other just by observing the two line segments but it is not sure.

Here we can clearly say that AB > CD but sometimes it is difficult to tell which one is greater.

2. Comparison by Tracing
In this method we have to trace one line on paper then put the traced line segment on the other line to check which one is greater.

3. Comparison using Ruler and a Divider
We can use a ruler to measure the length of a line segment.
Put the zero mark at point A and then move toward l to measure the length of the line segment, but it may have some errors on the basis of the thickness of the ruler. This could be made accurate by using a Divider.

• Put the one end of the divider on point A and open it to put another end on point B.
• Now pick up the divider without disturbing the opening and place it on the ruler so that one end lies on “0”.
• Read the marking on the other end and we can compare the two line.

Question for Short Notes: Understanding Elementary Shapes
Try yourself:What method is used to compare the length of line segments accurately?

## Angles – “Right” and “Straight”

We can understand the concept of right and straight angles by directions.
There are four directions-North, South, East and West.

• When we move from North to East then it forms an angle of 90° which is called Right Angle.
• When we move from North to South then it forms an angle of 180° which is called Straight Angle.
• When we move four right angles in the same direction then we reach to the same position again i.e. if we make a clockwise turn from North to reach to North again then it forms an angle of 360° which is called a Complete Angle. This is called one revolution.
• In a clock, there are two hands i.e. minute hand and hour hand, which moves clockwise in every minute. When the clock hand moves from one position to another then turns through an angle.
• When a hand starts from 12 and reaches to 12 again then it is said to be completed a revolution.

## Acute, Obtuse and Reflex Angles

There are so many other types of angles which are not right or straight angles.

## Measuring Angles

By observing an angle we can only get the type of angle but to compare it properly we need to measure it.

• An angle is measured in the “degree”. One complete revolution is divided into 360 equal parts so each part is one degree. We write it as 360° and read as “three hundred sixty degrees".
• We can measure the angle using a ready to use device called Protractor.
• It has a curved edge which is divided into 180 equal parts. It starts from 0° to 180° from right to left and vice versa.

Steps to measure an angle using protractor-

Step 1: Place the protractor on the angle in such a way that the midpoint of protractor comes on the vertex B of the angle.

Step 2: Adjust it so that line BC comes on the straight line of the protractor.

Step 3: Read the scale which starts from 0° coinciding with the line BC.

Step 4: The point where the line AB comes on the protractor is the degree measure of the angle.

Hence, ∠ABC = 72°.

## Perpendicular Lines

If two lines intersect with each other and form an angle of 90° then they must be perpendicular to each other.

Here AB and MN are intersecting at point N and form a right angle. We will write it as AB ⊥ MN or MN ⊥ AB Reads as AB is perpendicular to MN or MN is perpendicular to AB.

## Perpendicular Bisector

If a perpendicular divides another line into two equal parts then it is said to be a perpendicular bisector of that line.

Here, CD is the perpendicular bisector of AB as it divides AB into two equal parts i.e. AD = DB.

Question for Short Notes: Understanding Elementary Shapes
Try yourself:What is the condition for two lines to be perpendicular to each other?

## Classification of Triangles

Triangle is a polygon with three sides. It is the polygon with the least number of sides. Every triangle is of different size and shape. We classify them on the basis of their sides and angles.

1. Classification on the basis of sides

2. Classification on the basis of Angles

A polygon with four sides is called Quadrilateral.

## Polygons

Any closed figure made up of three or more line segments is called Polygon.
We can classify the polygons on the basis of their sides and vertices -

### Three-dimensional Shapes

The solid shapes having three dimensions are called 3D shapes.
Some of the 3D shapes around us

### Faces, Edges and Vertices

• All the flat surfaces of the solid shape are called the Faces of that figure.
• The line segment where the two faces meet with each other is called Edge.
• The point where the two edges meet with each other is called Vertex.

Question for Short Notes: Understanding Elementary Shapes
Try yourself:What is the name given to the point where two edges of a solid shape meet?

No. of Faces, Edges and Vertices in some common 3- D shapes

The document Understanding Elementary Shapes Class 6 Notes Maths Chapter 5 is a part of the Class 6 Course Mathematics (Maths) Class 6.
All you need of Class 6 at this link: Class 6

## Mathematics (Maths) Class 6

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## FAQs on Understanding Elementary Shapes Class 6 Notes Maths Chapter 5

 1. How do you measure line segments?
Ans. To measure a line segment, you can use a ruler or a measuring tape. Place the starting point of the line segment at the zero mark of the ruler or measuring tape. Then, align the end point of the line segment with the appropriate measurement mark on the ruler or measuring tape. Read the measurement where the line segment ends.
 2. What is the difference between a "right" angle and a "straight" angle?
Ans. A "right" angle measures exactly 90 degrees and is represented by a small square. It forms the corners of squares and rectangles. On the other hand, a "straight" angle measures exactly 180 degrees and is represented by a straight line. It is a line that does not bend or curve, forming a straight line.
 3. What are acute, obtuse, and reflex angles?
Ans. Acute angles are angles that measure less than 90 degrees. They are sharper angles and are commonly found in triangles. Obtuse angles measure more than 90 degrees but less than 180 degrees. They are wider angles and can be found in shapes like obtuse triangles or quadrilaterals. Reflex angles measure more than 180 degrees but less than 360 degrees. They are larger angles that exceed a straight angle.
 4. How do you measure angles?
Ans. To measure angles, you can use a protractor. Place the center of the protractor at the vertex of the angle. Align one side of the angle with the baseline of the protractor. Read the measurement where the other side of the angle intersects with the protractor's scale. The measurement is given in degrees.
 5. What are perpendicular lines and perpendicular bisectors?
Ans. Perpendicular lines are lines that intersect each other at a right angle (90 degrees). They form four right angles at the point of intersection. A perpendicular bisector is a line or line segment that divides another line segment into two equal parts at a right angle. It passes through the midpoint of the line segment and creates two congruent segments.

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