Pressure - Pascal's Principle

When riding a bicycle or driving a car, how do we come to a stop? By using the brakes, of course! But how does it work? 

You are either squeezing the brakes on the bicycle with your hands, or you’re stepping down on the brakes in your car with your feet. There doesn’t seem to be a direct connection from the brakes to the wheels on the bicycle except for a thin tube. So, what’s going on here?

“Pressure exerted on an enclosed liquid is transmitted uniformly throughout the liquid”
Pascal’s Principle

To make things simple, let’s picture the brakes on the bicycle. The force that you apply on the brakes generates a pressure within the enclosed liquid in the brakes system. Yes, the “thin tube” is actually filled with a liquid! This pressure is then transmitted equally throughout the liquid. Then, the force applied when you squeeze the brakes is multiplied at the wheels. How does this happen? Let’s explore.

Video lesson

Hydraulic system

The system used in brakes is known as the hydraulic system. This system operates based on Pascal’s principle.

Let’s use the diagram to go through the basic principles of the workings of a hydraulic system.

There are two pistons – X and Y. Piston X has a smaller area in contact with the fluid than piston Y. This is a key point in the system. 

  1. When a force is applied at piston X, a pressure is generated at X.
  2. According to Pascal’s principle, since the liquid is enclosed, the pressure generated at X is transmitted uniformly in all directions throughout the liquid in the hydraulic system.
  3. The pressure at piston Y is the same as the pressure at piston X.
  4. Using the equation in the diagram, we can find any one of the variables if the other 3 are given.

Hydraulic systems are used in:

  • hydraulic brakes
  • hydraulic jacks
  • hydraulic lifts

Hydraulic system as a force multiplier

In the last equation, it can be seen that the force at piston Y (F2) is the force at X (F1) multiplied by (A2/A1).

Therefore, the larger the area of the large piston (A2) compared to the area of the small piston (A1), the larger the multiple of F1 and the larger the force generated at piston Y!

Practice questions

Try out these questions to test your understanding of the topic.

Scroll to Top