Shapes and Measurements | Year 9 Mathematics (Cambridge) PDF Download

Properties of Shapes

Properties of 2D Shapes

2D shapes have length and width but no depth. They include squares, rectangles, circles, triangles, and polygons.
Key properties include:

• Sides and vertices: The number of edges (sides) and points where edges meet (vertices).
• Angles: The measure of the space between two intersecting lines. For example, squares have right angles (90 degrees), while triangles have angles that add up to 180 degrees.
• Symmetry: Lines of symmetry divide shapes into identical halves. A circle has infinite lines of symmetry, while a square has four.
• Examples:
  • A rectangle has 4 sides, 4 vertices, and 2 lines of symmetry.
  • A triangle can be equilateral (3 equal sides and angles), isosceles (2 equal sides and angles), or scalene (no equal sides or angles).

Properties of 3D Shapes

3D shapes have length, width, and depth. They include cubes, spheres, cylinders, cones, and pyramids.
Key properties include:

• Faces, edges, and vertices: Faces are the flat or curved surfaces, edges are the lines where faces meet, and vertices are points where edges meet.
• Volume and surface area: Volume measures the space inside the shape, while surface area measures the total area of all faces.
• Examples:
  • A cube has 6 equal square faces, 12 edges, and 8 vertices.
  • A sphere has no edges or vertices and one continuous curved surface.

Perimeter, Area, and Volume

Perimeter

• The perimeter is the total length of the boundaries of a 2D shape. It is calculated by adding the lengths of all sides.
• Examples:
  • Perimeter of a rectangle: P = 2(l + w), where l is length and w is width.
  • Perimeter of a square: P = 4a, where a is the length of a side.

Area

• The area is the amount of space inside a 2D shape. Different shapes have different formulas for calculating area.
• Examples:
  • Area of a rectangle: A = l × w.
  • Area of a triangle: 
  • Area of a circle: A = πr², where r is the radius.

Volume

• Volume measures the space a 3D object occupies. It is calculated using different formulas based on the shape.
• Examples:
  • Volume of a cube: V = a³.
  • Volume of a rectangular prism: V = l × w × h.
  • Volume of a cylinder: V = πr²h, where r is the radius and h is the height.

Transformations

Types of Transformations

Transformations change the position or size of shapes on a coordinate plane.
There are four main types:

• Translation: Sliding a shape without rotating or flipping it. The shape moves a certain distance in a given direction.
• Rotation: Turning a shape around a fixed point. The angle of rotation (measured in degrees) determines how far the shape turns.
• Reflection: Flipping a shape over a line (mirror line) to produce a mirror image.
• Dilation: Resizing a shape by scaling it up or down. The shape remains similar to the original, maintaining proportional dimensions.
• Examples:
  • Translating a triangle 3 units to the right and 2 units up.
  • Rotating a square 90 degrees clockwise around its center.
  • Reflecting a rectangle over the y-axis.
  • Dilating a circle with a scale factor of 2 (doubling its size).

Conclusion

Understanding the properties of shapes, as well as how to calculate perimeter, area, and volume, is crucial in geometry. Transformations help us visualize and manipulate shapes in different ways. Mastering these concepts provides a solid foundation for more advanced mathematical studies.