Understanding Elementary Shapes

A line segment is a part of a line that has two distinct endpoints. It has a definite length. We measure the length of a line segment using a ruler.

An angle is formed when two rays meet at a common endpoint. The common endpoint is called the vertex, and the two rays are called the arms of the angle. Angles are measured in degrees (°). We use a protractor to measure angles.

Angles are classified based on their measure:\n* Acute Angle: An angle whose measure is greater than 0° but less than 90°.\n* Right Angle: An angle whose measure is exactly 90°.\n* Obtuse Angle: An angle whose measure is greater than 90° but less than 180°.\n* Straight Angle: An angle whose measure is exactly 180°. It forms a straight line.\n* Reflex Angle: An angle whose measure is greater than 180° but less than 360°.\n* Complete Angle: An angle whose measure is exactly 360°. It represents a full rotation.

Triangles are classified based on the lengths of their sides:\n* Scalene Triangle: A triangle in which all three sides have different lengths.\n* Isosceles Triangle: A triangle in which two sides have equal lengths.\n* Equilateral Triangle: A triangle in which all three sides have equal lengths. All angles in an equilateral triangle are also equal (60° each).

Triangles are classified based on the measure of their angles:\n* Acute-angled Triangle: A triangle in which all three angles are acute angles (less than 90°).\n* Right-angled Triangle: A triangle in which one of the angles is a right angle (exactly 90°).\n* Obtuse-angled Triangle: A triangle in which one of the angles is an obtuse angle (greater than 90°).

Shapes that have length, breadth, and height (or depth) are called three-dimensional shapes. They occupy space. Common 3D shapes include cuboids, cubes, cylinders, cones, and spheres.\n* Faces: The flat surfaces of a 3D shape.\n* Edges: The line segments where two faces meet.\n* Vertices: The corners where three or more edges meet.

* Cuboid: A solid shape with 6 rectangular faces, 12 edges, and 8 vertices. Example: a brick.\n* Cube: A special type of cuboid where all 6 faces are square and all edges are of equal length. It has 6 faces, 12 edges, and 8 vertices. Example: a dice.\n* Cylinder: A solid shape with two circular bases and one curved surface. It has 3 faces (2 flat, 1 curved), 2 curved edges, and 0 vertices. Example: a cold drink can.\n* Cone: A solid shape with one circular base and one curved surface that tapers to a single point (vertex). It has 2 faces (1 flat, 1 curved), 1 curved edge, and 1 vertex. Example: an ice-cream cone.\n* Sphere: A perfectly round 3D object where every point on its surface is equidistant from its centre. It has 1 curved face, 0 edges, and 0 vertices. Example: a football.\n* Pyramid: A solid shape with a polygonal base and triangular faces that meet at a common vertex (apex). A square pyramid has a square base, 5 faces (1 square, 4 triangular), 8 edges, and 5 vertices.