A physical connection is a direct mechanical or wired link that transfers force, motion, or signal between parts. In engineering, it gives a system a predictable, inspectable control path: a cable, linkage, or connector does exactly what its path allows. In the bicycle-brake example, a physical connection gives the rider immediate, visible feedback and reduces dependence on hidden electronics.
In cyber security, physical connections matter because they define what an attacker can touch, unplug, intercept, or tamper with. Defenders often prefer direct links for critical functions when they want less software complexity and fewer wireless attack surfaces. Attackers, however, may exploit exposed ports, cut cables, insert hardware implants, or bypass controls by manipulating the physical layer. Good defense means protecting connectors, monitoring integrity, and designing safe fallback behavior if the link is broken.