Circles in Modern Life

Radar sweeps in circles. Satellites orbit in near-circles. CT scanners rotate X-ray sources in circles around patients to build 3D images. Roundabouts move traffic in circles for efficiency. The circle's constant curvature makes it the natural choice for anything that rotates.

Even non-physical circles matter. Pie charts divide a circle by percentage to visualize data. Circular reasoning in logic (assuming your conclusion) is named for the shape because the argument goes nowhere — it returns to where it started.