According to hydraulic principles, what happens when pressure is applied to the brake pedal?

When pressure is applied to the brake pedal, the hydraulic principles governing the braking system come into play, resulting in an increase in pressure within the hydraulic lines. This is rooted in Pascal's Law, which states that when pressure is applied to a confined fluid, that pressure is transmitted undiminished throughout the fluid.

As the driver presses the brake pedal, a piston in the master cylinder compresses the brake fluid. This action directly increases the pressure in the hydraulic lines connected to the brakes. The heightened pressure then facilitates the movement of additional pistons at the brake calipers or wheel cylinders, which in turn causes the brake pads to clamp down on the rotors or drums, creating the friction necessary to slow down or stop the vehicle.

In this scenario, the other options do not accurately depict what occurs in the hydraulic brake system under pressure. An increase in pressure is essential for effective braking, highlighting the correct response to the question.