Final answer:
During normal driving, spring brakes are held back by spring pressure.
Step-by-step explanation:
The correct answer is option A) spring pressure.
During normal driving, spring brakes are held back by the spring pressure. The spring in the brake system helps to apply and release the brakes. When the brake pedal is pushed, it compresses the spring, and when the pedal is released, the spring pressure helps to release the brakes.
For example, in hydraulic brakes, the force applied by the driver on the brake pedal is increased by a lever and the hydraulic system. This increased force is used to compress the spring and initiate the braking action. When the pressure on the pedal is released, the spring pressure helps in releasing the brakes.
Typically, in hydraulic brake systems, the spring brakes are held back, or released, by means of pressurized air. When a driver operates the vehicle under normal conditions, air pressure within the brake system counteracts the force of the springs. This is essential for allowing the brakes to disengage so the vehicle can move freely.
Without sufficient air pressure, the spring brakes would engage, preventing the wheels from turning.
This system relies on the principles of hydraulics, as outlined by Pascal's Principle, which states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.
Hydraulic systems in vehicles are designed to multiply the force applied by the driver on the brake pedal, enabling a much greater force to be applied to the wheel cylinders.
This design takes into account friction, the normal force, and other factors to ensure consistent braking power. In short, air pressure is the crucial element holding back the spring brakes during regular vehicle operation.