What is the purpose of the master cylinder in a brake system?

The master cylinder plays a critical role in the brake system by converting the force applied to the brake pedal into hydraulic pressure. When you press the brake pedal, the master cylinder compresses the brake fluid inside it. This compression creates hydraulic pressure that travels through the brake lines to the brake calipers or drums, which then engages the brakes to slow down or stop the vehicle. This hydraulic mechanism allows for more efficient braking, as it multiplies the force applied by the driver.

The other options do not encompass the function of the master cylinder. Measuring vehicle speed is typically the role of a speedometer; storing brake fluid is a secondary function of other components in the brake system; and controlling engine performance pertains to systems that manage combustion and power output, which is unrelated to the braking function.