pplications

The underlying principle of the hydraulic press

Used for amplifying the force of the driver's foot in the braking system of most cars and trucks.
Used in artesian wells, water towers, and dams.
Scuba divers must understand this principle. At a depth of 10 meters under water, pressure is twice the
atmospheric pressure at sea level, and increases by about 105 kPa for each increase of 10 m depth.
Applications of Pascal's Principle in Everyday Life
A hydraulic system is a device in which a small applied force can give rise to a
larger force.

The principle in the hydraulic system is widely used in jacks, vehicle brake
systems, hydraulic presses and heavy machinery and a few more examples which
you can find (for yourself)

Hyraulic Jacks

Hydraulic jacks are used to lift a heavy load such as when changing a car tyre.
When the handle is pressed down, a valve closes and the small piston forces
hydraulic fluid through another valve to the larger cylinder. The pressure
transmitted results in a large force on the load.



When the handle is raised, valve B closes and hydraulic fluid flows from the buffer
tank through valve A into the small cylinder. The handle is moved up and down
repeatedly until the load is sufficiently lifted up.

The large piston can be lowered at the end by opening the release valve to allow
all the hydraulic fluid to flow back into the buffer tank.

Hydraulic Brakes

Hydraulic brakes are used in cars, lorries and motorcycles.

In a hydraulic brake system, a liquid, known as brake fluid,
is used to transmit pressure from the brake pedal to all the wheels of the vehicle.


When the brake pedal is pressed, the piston of the control cylinder applies a
pressure on the brake fluid and this pressure is transmitted, via a system of pipes,
to each cylinder at the wheels.

The cylinder at the wheels cause a pair of pistons to push a pair of friction pads to
press against the surface of the brake discs or brake drums. The frictional forces
between these brake components cause the vehicle to slow down and stop.

When the brake pedal is released, a spring restores the brake discs to their original
positions.

Hydraulic Pumps

Hydraulic pumps are used to raise cars in a motor workshop.

The machine is equipped with a small cylinder connected to a large cylinder. Both
cylinders are filled with oil.

Compressed air is introduced into the small cylinder in which the compressed air
exerts a pressure on the surface of the oil.

This pressure is transmitted by the oil to the large cylinder where the pressure
acts on a large piston to produce a force which is large enough to lift a car.

Hope this helps!
Application of Pascals Principle
One of the most important technological applications of Pascals principle is found in a hydraulic
system, which is an enclosed fluid system used to exert forces. The most common hydraulic
systems are those that operate car brakes. Let us first consider the simple hydraulic system
shown in Figure.
A typical hydraulic system with two fluid-filled cylinders,
capped with pistons and connected by a tube called a hydraulic line. A downward force F1 on the left
piston creates a pressure that is transmitted undiminished to all parts of the enclosed fluid. This results
in an upward force F2 on the right piston that is larger than F1 because the right piston has a larger
area.
Relationship Between Forces in a Hydraulic System
We can derive a relationship between the forces in the simple hydraulic system shown
in Figure by applying Pascals principle. Note first that the two pistons in the system are at the
same height, and so there will be no difference in pressure due to a difference in depth. Now the
pressure due to F1 acting on area A1 is simply P1=F1A1, as defined by P=FA. According to
Pascals principle, this pressure is transmitted undiminished throughout the fluid and to all walls
of the container. Thus, a pressure P2 is felt at the other piston that is equal to P1. That is P1=P2.
But since P2=F2A2, we see that F1A1=F2A2.
This equation relates the ratios of force to area in any hydraulic system, providing the pistons are
at the same vertical height and that friction in the system is negligible. Hydraulic systems can
increase or decrease the force applied to them. To make the force larger, the pressure is applied
to a larger area. For example, if a 100-N force is applied to the left cylinder in Figure and the
right one has an area five times greater, then the force out is 500 N. Hydraulic systems are
analogous to simple levers, but they have the advantage that pressure can be sent through
tortuously curved lines to several places at once.
Calculating Force of Slave Cylinders: Pascal Puts on the Brakes
Consider the automobile hydraulic system shown in Figure.
Hydraulic brakes use
Pascals principle. The driver exerts a force of 100 N on the brake pedal. This force is increased by the
simple lever and again by the hydraulic system. Each of the identical slave cylinders receives the same
pressure and, therefore, creates the same force output F2. The circular cross-sectional areas of the
master and slave cylinders are represented by A1 and A2, respectively
A force of 100 N is applied to the brake pedal, which acts on the cylindercalled the master
through a lever. A force of 500 N is exerted on the master cylinder. (The reader can verify that
the force is 500 N using techniques of statics from Applications of Statics, Including Problem-
Solving Strategies.) Pressure created in the master cylinder is transmitted to four so-called slave
cylinders. The master cylinder has a diameter of 0.500 cm, and each slave cylinder has a
diameter of 2.50 cm. Calculate the force F2 created at each of the slave cylinders.
Strategy
We are given the force F1 that is applied to the master cylinder. The cross-sectional
areas A1 and A2 can be calculated from their given diameters. Then F1A1=F2A2 can be used to find
the force F2. Manipulate this algebraically to get F2 on one side and substitute known values:
Solution
Pascals principle applied to hydraulic systems is given by F1A1=F2A2:
F2=A2A1F1=r22r21F1=(1.25 cm)2(0.250 cm)2500 N=1.25104N.
Discussion
This value is the force exerted by each of the four slave cylinders. Note that we can add as many
slave cylinders as we wish. If each has a 2.50-cm diameter, each will exert 1.25104N.
A simple hydraulic system, such as a simple machine, can increase force but cannot do more
work than done on it. Work is force times distance moved, and the slave cylinder moves through
a smaller distance than the master cylinder. Furthermore, the more slaves added, the smaller the
distance each moves. Many hydraulic systemssuch as power brakes and those in bulldozers
have a motorized pump that actually does most of the work in the system. The movement of the
legs of a spider is achieved partly by hydraulics. Using hydraulics, a jumping spider can create a
force that makes it capable of jumping 25 times its length!
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