Each brake contains a slave cylinder with a piston inside it. The rising pressure in the hydraulic fluid exerts a force on the slave cylinder's piston. The pistons of the slave cylinders will move half as far as the piston of the master cylinder. If they didn't have to share, their pistons would move exactly as far as the piston of the master cylinder. But since they do share, each of these cylinders receives half the hydraulic fluid that leaves the master cylinder and the piston in each slave cylinder moves half as far as the piston in the master cylinder.
Air compresses easily as the pressure inside the brake lines increases.
When you push the brake pedal down and squeeze brake fluid out of the master cylinder, the slave cylinders don t respond properly. As the pressure in the hydraulic system rises, the air bubble will compress and its volume will shrink. Some of the hydraulic fluid flowing out of the master cylinder will go to filling the space vacated by the shrinking gas bubble, rather than to filling the slave cylinders. A one-wheeled cycle, or unicycle, is the ultimate in statically unstable vehicles. As a result, its gravitational potential energy decreases and an object naturally accelerates in the direction that reduces its potential energy as quickly as possible.