Perimeter

Hello there. Have you ever traced the edge of a cookie with your finger before taking a bite? Or run your hand along a fence as you walk down the street? That line you're following, that path around the very edge of things... that's me. I am the invisible line that hugs the outside of your favorite picture frame, the chalk line that marks the edge of a baseball field, and the delicious crust on a slice of pizza. Before you knew my name, you knew what I did. I show you where things begin and end. I am the outline, the border, the edge of everything. Can you guess who I am? I am Perimeter.

For a long, long time, even before there were schools like yours, people needed me. Imagine you were a farmer in ancient Egypt, thousands of years ago. Every single year, a giant river called the Nile would flood its banks, and the rushing water would wash away all the stones and markers for your fields. When the water finally went down, leaving behind rich, dark mud for planting, how would you know which piece of land was yours and which was your neighbor's? It was a huge problem. You'd need me. Farmers would take long ropes with knots tied at even spaces and walk along the edges of their land. By counting the knots, they could measure the distance all the way around their fields and make sure their fences and markers were put back in exactly the right place. They were using me, Perimeter, to bring order back to their world. Later, in ancient Greece, some very clever thinkers gave me my official name. They looked at what I did and put two words together: 'peri,' which means 'around,' and 'metron,' which means 'measure.' So, my name literally means 'to measure around.' A famous man named Euclid, who wrote a huge book all about shapes around 300 BCE, loved to figure out the rules for how I work. He and others discovered that for a perfect square, you just had to add up the lengths of its four equal sides. For a rectangle, you add up its two long sides and two short sides. They turned a farmer's clever trick into a powerful idea in the world of mathematics, a subject they called geometry.

Today, you can find me everywhere, helping people create and organize the world you live in. When an architect designs a brand-new house, they use me to figure out exactly how much wood they need for the walls and how long a fence should be for the backyard. When a city planner designs a new park, they use me to map out the winding walking trails, the border for the playground, and the edges of the colorful garden beds. I'm there in the bright white lines of a soccer field, telling players exactly where the game is played. I'm even inside your computer and video game consoles, helping to define the boundaries of your favorite digital world. I am the simple but very important idea of measuring the distance around something. I help you put a frame on your art, a fence around your yard, and a border around your ideas. The next time you walk around the block or trace the edge of a book with your finger, give me a little wave. I'll be there, helping you measure and understand the shape of your amazing world.