In our surroundings, numerous forms composed of lines and curves can be observed, such as line segments, angles, triangles, polygons, and circles, among others. These shapes vary in both size and dimensions.
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. The length of a line segment is the distance between its endpoints.
Line Segment
In this section, the focus is on understanding and measuring line segments.
Comparison by Observation:
Comparison by Observation
Comparison by Tracing:
Comparison using Ruler and a Divider
This could be made accurate by using a Divider.
Using a divider
Right angle: The measure of a right angle is 90° and hence that of a straight angle is 180°.
Straight angle: An angle whose measure is 180°.
Right and Straight Angles
When we move from North to South then it forms an angle of 180° which is called Straight Angle. revolution is a straight angle.
Directions
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.
 Acute angle: An angle whose measure is more than 0° but less than 90°. Seasaw, rooftop, opening book, etc. are examples of an acute angle.
 Obtuse angle: An angle whose measure is more than 90° but less than 180°. House, desk for book reading, etc. are examples of an obtuse angle.
 Reflex angle: An angle whose measure is more than 180° but less than 360° is called a reflex angle. A reflex angle is larger than a straight angle.
 Complete angle: An angle whose measure is 360°, is called a complete angle.
Types of Angles
To understand angles better, we don't just look at them, we measure them! We use a special unit called "degrees" to measure angles.
ProtactorTo measure an angle using protractor
When two lines intersect and the angle between them is a right angle, then the lines are said to be perpendicular. If a line AB is perpendicular to CD, we write AB ⊥ CD.
Perpendicular Lines
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.
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.
Types of Triangles based on Sides
(i) Equilateral triangle: A triangle having all sides equal, is called an equilateral triangle.
(ii) Isosceles triangle: A triangle having two sides equal, is called an isosceles triangle.
(iii) Scalene triangle: A triangle having all sides of different lengths is called a scalene triangle.
Types of Triangles based on Angles
(i) Acute triangle: A triangle each of whose angle measures less than 90° is called an acute triangle.
(ii) Right angled triangle: A triangle one of whose angle measures 90° is called a right angled triangle.
(iii) Obtuse triangle: A triangle one of whose angle measures more than 90° is called an obtuse triangle.
A plane figure bounded by four line segments is called a quadrilateral.
Types of Quadrilaterals
Polygon is a closed figure bounded by three or more than three line segments.
Types of Polygons
The solid shapes having three dimensions are called 3D shapes.
3D shapes around us
134 videos323 docs42 tests

1. How can elementary shapes be classified? 
2. What is the difference between a 2D shape and a 3D shape? 
3. How can we identify different shapes in our surroundings? 
4. Why is it important to understand elementary shapes? 
5. How can we use elementary shapes to create composite shapes? 

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