Understanding Elementary Shapes

- The distance between the end points of a line segment is its length.

- A graduated ruler and the divider are useful to compare lengths of line segments.

- When a hand of a clock moves from one position to another position we have an example for an angle.

- One full turn of the hand is 1 revolution.

- A right angle is ¼ revolution and a straight angle is ½ a revolution.

- We use a protractor to measure the size of an angle in degrees.

- The measure of a right angle is 90° and hence that of a straight angle is 180°.

- An angle is acute if its measure is smaller than that of a right angle and is obtuse if its measure is greater than that of a right angle and less than a straight angle.

- A reflex angle is larger than a straight angle.

- Two intersecting lines are perpendicular if the angle between them is 90°.

- The perpendicular bisector of a line segment is a perpendicular to the line segment that divides it into two equal parts.

- Triangles can be classified as follows based on their angles:

Each angle is acute: Acute angled triangle

One angle is a right angle: Right angled triangle

One angle is obtuse: Obtuse angled triangle

Triangles can be classified as follows based on the lengths of their sides:
- Scalene triangle: All the three sides are of unequal length

Isosceles triangle: Any two of the sides are of equal length

Equilateral triangle: All the three sides are of equal length

Polygons are named based on their sides.

3: Triangle

4: Quadrilateral

5: Pentagon

6: Hexagon

8: Octagon

Quadrilaterals are further classified with reference to their properties.

One pair of parallel sides: Trapezium

Two pairs of parallel sides: Parallelogram

Parallelogram with 4 right angles: Rectangle

Parallelogram with 4 sides of equal length: Rhombus

A rhombus with 4 right angles: Square

We see around us many three dimensional shapes. Cubes, cuboids, spheres, cylinders, cones, prisms and pyramids are some of them.