Grade 6 → Mensuration → Perimeter ↓
Perimeter of Simple Shapes
The perimeter of a shape is the distance around its edges. Imagine you are walking in a park that is shaped like a square. The perimeter would be the total distance you walk to get around the park.
Understanding the perimeter
Perimeter is a useful measurement that helps us understand the size of the boundary of simple shapes. Whether it is fencing around a garden or drawing a picture, knowing the perimeter gives us the necessary information.
Perimeter of a square
A square is a simple shape with four equal sides. To find the perimeter of a square, you add the lengths of the four sides. Since all sides are equal, you can simply multiply the length of one side by 4.
Formula for the perimeter of a square:
Perimeter = 4 × side length
Example: If the side of a square is 5 units:
Perimeter = 4 × 5 = 20 units
Perimeter of a rectangle
The opposite sides of a rectangle are equal. The perimeter of a rectangle is the sum of all its sides, which can be calculated using the lengths of the opposite sides.
Formula for the perimeter of a rectangle:
Perimeter = 2 × (length + breadth)
Example: If the length is 8 units and the width is 3 units:
Perimeter = 2 × (8 + 3) = 2 × 11 = 22 units
Perimeter of a triangle
A triangle has three sides. To find its perimeter, add up the lengths of the three sides.
Formula for the perimeter of a triangle:
Perimeter = side1 + side2 + side3
Example: If the sides of a triangle are 5 units, 6 units, and 7 units:
Perimeter = 5 + 6 + 7 = 18 units
Circumference (Circumference) of a circle
Although a circle doesn't have sides like polygons, it does have a boundary that we measure. The perimeter of a circle is known as the circumference. To calculate the circumference, you need the radius or diameter of the circle.
Formula of Perimeter:
Circumference = 2 × π × radius
Or
Circumference = π × diameter
Here, π (pi) is approximately 3.14159.
Example using radius: If the radius is 4 units:
Perimeter = 2 × π × 4 = 8π ≈ 25.13 units
Example using diameter: If the diameter is 10 units:
Perimeter = π × 10 = 10π ≈ 31.42 units
Practical applications of perimeter
Knowing how to calculate the perimeter of different shapes can have many practical applications. Here are some examples:
- If you need to put a fence around a rectangular piece of land, knowing the perimeter can help you buy the right amount of fencing materials.
- When building a track for walking or running, the perimeter can help determine how long the path needs to be to reach the desired distance.
- Framing a picture or painting requires knowledge of the perimeter to ensure the frame fits properly.
Challenges and exercises
Here are some exercises to practice the concept of perimeter. Try solving them yourself!
Exercise 1:
You have a rectangular shaped garden. Its length is 12 units and width is 7 units. What is the perimeter of the garden?
Exercise 2:
A square board game needs a border. If one side of the board is 15 units, how much material will be needed to make the border?
Exercise 3:
The lengths of the sides of a triangular park are 9 units, 12 units and 15 units. Calculate the total length of the fence required to enclose the park.
Conclusion
Understanding the perimeter of simple shapes is a basic skill in geometry and math. By practicing and experimenting with these concepts, students can gain confidence in their ability to measure and work with different shapes. The formulas are straightforward, but they are incredibly useful in solving real-world problems.