When pressure is applied to a fluid in a sealed container, the pressure is transmitted equally in all directions throughout the fluid.
Liquids such as water or oil, when enclosed and pressed, seek no escape and distribute the applied force evenly. Because liquids are nearly incompressible, the pressure is conveyed uniformly without a significant loss of force.

Although the pressure applied to a fluid remains the same, the force increases when it acts on a larger surface area.
Pressure (Pa) = Force (N) ÷ Area (m²)
Force (N) = Pressure (Pa) × Area (m²)

This principle is utilized in braking systems. When the brake pedal is pressed, a small piston pushes the brake fluid, generating pressure. This pressure is transmitted through the hydraulic lines to a larger piston. The force is thus amplified, allowing the larger piston to press the brake pads against the brake rotor and bring the vehicle to a stop.

Gases, like liquids, also transmit pressure in all directions. However, since gases are more compressible than liquids, the transmission of pressure can vary, making gases less stable and precise for certain applications.

This property of gases is used in tires. When air is pumped into a tire, the pressure expands evenly throughout the interior. As a result, the same force is exerted on all inner surfaces of the tire, allowing it to maintain its shape and support the weight of the vehicle.

Why Automotive Systems Use Oil Rather Than Water

There are several important reasons why oil is used in automotive systems instead of water. While water may seem like a convenient fluid, it lacks many of the essential properties required for safe and reliable operation.

• Lubricating Properties
  • Oil acts as a lubricant between moving parts, helping to reduce friction and wear. This extends the lifespan of mechanical components.
  • Water, on the other hand, does not provide lubrication and can lead to rapid wear and damage to metal parts.
• Corrosion Prevention
  • Water can cause metal components to rust over time.
  • In contrast, oil forms a protective coating on surfaces, helping to prevent corrosion and maintain the integrity of the system.
• High Boiling Point and Resistance to Evaporation
  • Oil has a much higher boiling point than water, which allows it to remain stable even under high temperatures.
  • Water, which evaporates easily, is not suitable for use in high temperature situations such as braking.
• Appropriate Viscosity
  • Oil has a higher viscosity than water, making it less likely to leak through small gaps.
  • However, if the oil is too thick, it can hinder smooth movement. For this reason, oils used in hydraulic systems are carefully formulated to have the right balance of viscosity for efficient operation.
• Resistance to Freezing
  • Water freezes at 0°C, which can cause severe problems in colder climates.
  • Oil, however, is far less likely to freeze under normal environmental conditions, making it more reliable in a wide range of temperatures.