Final answer:
The brake caliper is responsible for physically applying the outboard pad in a floating caliper disc brake system. The brake caliper moves and clamps the rotor between the inboard and outboard pads when force is transferred from the brake fluid.
Step-by-step explanation:
In a floating caliper disc brake system, the part that physically applies the outboard pad is the brake caliper. When the brake pedal is pressed by the driver, a force is exerted that is increased through a mechanical lever and even more so by the hydraulic system based on Pascal's principle. The brake fluid in the system transfers this force to the brake caliper. This causes the caliper, which is able to move slightly on its mounts, to press into the inboard side of the rotor with the inboard pad due to the force exerted by the brake piston. This action, in turn, pulls the caliper and hence the outboard pad towards the other side of the rotor to apply the braking force on both sides of the disc. It is essential to understand that while the brake piston directly presses the inboard pad, it is the movement of the caliper itself that allows the outboard pad to come into contact with the brake rotor.