Cogs are circular, toothed wheels that work together in machines to transmit motion and force. They are essential components in various mechanical systems, including clocks, engines, and gearboxes. When one cog turns, it engages with another cog, causing it to rotate as well, which helps to transfer energy and control speed. Cogs come in different sizes and shapes, depending on their specific function in a machine. They are often made from materials like metal or plastic to ensure durability and efficiency. The arrangement of cogs in a system is crucial for achieving the desired mechanical advantage and performance in devices like bicycles and automobiles.