How The Car Brake Works

We all know that pushing down on the brake pedal slows a car to a stop. The brakes are designed to slow down your vehicle but probably not by the means that you think. The common misconception is that brakes squeeze against a drum or disc, and the pressure of the squeezing action is what slows you down. This in fact is only part of the equation.

  Brakes are essentially a mechanism that leads to change in energy types. But how does this happen? How does your car transmit the force from your leg to its wheels? How does it multiply the force so that it is enough to stop something as big as a car?

 Lets talk about the way the brake works from two perspectives

• Energy conversion that leads to the breaking action and 

• The mechanical point of view of the braking action.

 Energy Conversion of the braking action.

 When you're traveling with any speed, your vehicle has kinetic energy. When you apply the brakes, the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction. The cooling of the brakes dissipates the heat and the vehicle slows down. It's the First Law of Thermodynamics, sometimes known as the law of conservation of energy. This states that energy cannot be created nor destroyed, it can only be converted from one form to another. In the case of brakes, it is converted from kinetic energy to thermal energy.
Mechanical Process of the braking action
  When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot. It does this in two ways:

• Mechanical advantage (leverage)
• Hydraulic force multiplication

­The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using three principles:

• Leverage
• Hydraulics
• Friction

Leverage and Hydraulics

This explains how a very little force fro your leg can cause a very large force to stop a car of so many tonnes. Well lets explain how that can be possible using the PRINCIPLE OF MOMENT OF FORCES and LEVER.

 F   X   D   =   f   X   d,   

If  D = 2 X d , Then

             f  =  2 X  F

In this principles we get to learn that when a force F is being applied to the left end of the lever. The left end of the lever is twice as long (2X) as the right end (X). Therefore, on the right end of the lever a force of 2F is available, but it acts through half of the distance (Y) that the left end moves (2Y). Changing the relative lengths of the left and right ends of the lever changes the multipliers. So force can be increased by varying the lever distances. However in the brake system it goes into hydraulics, not just lever
 
The basic idea behind any hydraulic system is very simple like that of the lever: Force applied at one point is transmitted to another point using an incompressible fluid, almost always an oil of some sort. Most brake systems also multiply the force in the process. Consider a simple hydraulic system

In the figure , two pistons (shown in brown) are fit into two glass cylinders filled with oil (shown in light blue) and connected to one another with an oil-filled pipe. If you apply a downward force to one piston (the left one, in this drawing), then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good -- almost all of the applied force appears at the second piston. The great thing about hydraulic systems is

• The force transferred to the right cylinder is greater than than in the left because pressure is constant in all part of the fluid so since the right cylinder has a larger surface area it will yield a bigger force to maintain constant pressure like the smaller cylinder.

• The pipe connecting the two cylinders can be any length and shape, allowing it to snake through all sorts of things separating the two pistons. The pipe can also fork, so that one master cylinder can drive more than one slave cylinder if desired, as shown in here:

To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r². The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).
Next, we'll look at the role that friction plays in brake systems

 Friction

Friction is a measure of how hard it is to slide one object over another. when these surfaces slide against each other, their weight presses their rough edges together ( microscopic in very smooth materials like glass).
So the amount of force it takes to move a given block is proportional to that block's weight. The more weight, the more force required. This concept applies for devices like brakes and clutches, where a pad is pressed against a spinning disc. The more force that presses on the pad, the greater the stopping force.

How the Brake Works

In theory...

Imagine how much force you need to stop a fast-moving car. Simply pressing with your foot would not generate enough force to apply all four brakes hard enough to bring you quickly to a stop. That's why brakes use hydraulics: a system of fluid-filled pipes that can multiply force and transmit it easily from one place to another as discussed earlier.

When you press on the brake pedal, your foot moves a lever that forces a piston into a long, narrow cylinder filled with hydraulic fluid. As the piston plunges into the cylinder, it squirts hydraulic fluid out through a long and narrow pipe at the end (much like squirting a syringe). The narrow pipe feeds into much wider cylinders positioned next to the car's four brakes. Because the cylinders near the brakes are much wider than the one near the brake pedal, the force you originally applied is multiplied greatly, clamping the brakes hard to the wheels. So there is more than one force multiplier;

• that of the lever which is the transmitted to the piston

• that of the piston which is then transmitted to the brake pads.

This explains why the small force from your leg on the pedal can create such great force at the brake pad to stop the car.

In practice...

1. Your foot pushes on the brake pedal.
2. As the pedal moves down, it pushes a class 2 lever (a kind of simple machine), increasing your pushing force.
3. The lever pushes a piston (blue) into a narrow cylinder filled with hydraulic brake fluid (red). As the piston moves into the cylinder, it squeezes hydraulic fluid out of the end (like a bicycle pump squeezes out air).
4. The brake fluid squirts down a long, thin pipe until it reaches another cylinder at the wheel, which is much wider.
5. When the fluid enters the cylinder, it pushes the piston in the wider cylinder (blue) with greatly increased force.
6. The piston pushes the brake pad (green) toward the brake disc (gray).
7. When the brake pad touches the brake disc, friction between the two generates heat (red cloud).
8. The friction slows down the outer wheel and tire, stopping the car.

The brake pedal actually operates four separate hydraulic lines running to all four wheels. We're just showing one wheel here for simplicity.

We acknowledge the information and picture we gathered from explainthatstuff.com and howstuffworks.com