PHYSICS

A rolling wheel is not just sliding and not just spinning. It is both at once. The center of the wheel moves forward in a straight line while the rim rotates around that center. Every point on the rim follows a curved path called a cycloid. Rolling is one of humanity's most important inventions because it turns rotation into smooth travel with less effort than dragging. Carts, cars, bikes, and conveyor belts all depend on this combined motion. To understand a wheel fully, you must track translation of the whole object and rotation about its center together.