Circles are present in real life, both in the natural world and in manmade creations. Manicouagan Reservoir in Canada is a ring-shaped lake that formed in the remains of a crater. Mushrooms with domed caps have circular bases. Ferris wheels take the circle to vertical heights at amusement parks and carnivals. Many household items, including cups, candles, and doorknobs have circles in their designs.

**What Are Circles?**

A circle is a geometric shape defined as a set of points that are equidistant from a single point on the plane. The connected dots form a series of arcs that surround the center point. Although the perimeter of a circle has no straight lines, straight lines do play a part in calculations. A line between any point in the circle and the center point is called a radius. The circumference of the circle is the perimeter of the circle.

**A****rchitecture**

Circles appear frequently in architecture around the world. Domes, like those that top the United States Capitol in Washington, D.C., the Duomo of the Florence Cathedral, and St. Peter's Basilica in Vatican City are all examples of circles used in architecture. Architects also use circles as decorative features in their buildings. For example, the library at Phillips Exeter Academy in New Hampshire has towering slabs of concrete with circles cut out to let viewers see the stacks of books on each floor. The Chartres Cathedral in France features a large circular-shaped window above the front door.

**S****cience**

One application of circles in science is in the design of particle separators. The Large Hadron Collider in Europe is a tunnel in the shape of a circle. This shape helps force the particles to move. NASA uses pi ― the ratio of the circumference to the diameter ― in several applications. This includes calculation trajectories, determining the size of distant planets, and measuring craters.

**C****onstruction**

The Roman arch is one of the most famous examples of how circles are used in construction. Roman architects used wedge-shaped blocks to create the arches that supported their massive aqueducts and domed ceilings. These arches were able to support more weight than the vertical posts and horizontal support beams used in other buildings. Today, arches are still common in construction for this reason.

**T****ransportation**

The invention of the wheel remains one of the most important inventions of all time. This circle made it possible for people to move and move things greater distances at faster speeds. Circles are still evident in transportation where they appear in vehicle tires, roundabouts in roads, engine crankshafts, and road designs. GPS also relies on circles when determining distance. It identifies points and calculates the distance between the satellite and the point using a circle theory.

**V****ideo Games**

Video game creators rely on geometric concepts, including circle theorems when developing virtual worlds for their games. This is how they create the pathways characters follow to navigate around objects. They use their knowledge of circles to transfer two-dimensional ideas to a three-dimensional format.