Fields and Fences - Concept of Perimeter

Perimeter is the total length of the boundary of a closed shape. Imagine walking along the edges of a field until you return to the starting point; the distance covered is the perimeter.

For any closed figure made of straight lines, the perimeter is calculated by adding the lengths of all its sides together. For example, a triangle with sides $3\text{ cm}$, $4\text{ cm}$, and $5\text{ cm}$ has a perimeter of $3 + 4 + 5 = 12\text{ cm}$.

A rectangle has four sides where the opposite sides are equal in length. Visually, it has two identical long sides called Length ($L$) and two identical shorter sides called Breadth ($B$). To find its perimeter, you add all four: $L + B + L + B$.

A square is a shape where all four sides are exactly the same length. Visually, it looks perfectly symmetrical from all directions. Instead of adding the same side four times, we can simply multiply the length of one side by $4$.

Perimeter is measured in linear units. Common units used in CBSE Grade 4 include centimeters ($cm$), meters ($m$), and kilometers ($km$). If the sides are in meters, the perimeter must also be expressed in meters.

Fencing is a real-world application of perimeter. If you need to put a wire fence or a wooden border around a garden, the length of the material required is equal to the perimeter of that garden.

Perimeter only applies to closed shapes. An open shape, like a curved line that doesn't meet its starting point, does not have a defined perimeter in the same way a closed field does.

Different shapes can have the same perimeter. For example, a square with side $5\text{ cm}$ (Perimeter $20\text{ cm}$) and a rectangle with length $6\text{ cm}$ and breadth $4\text{ cm}$ (Perimeter $20\text{ cm}$) both have the same boundary length.