Hydraulic system called hydraulic jack. In this system a small, force F1 is applied on a small piston which produces pressure P on the oil. Pressure P is transmitted through the pipe to a very large cylinder fitted with a piston. Since area of this piston is very huge. So, a very large force is produced by pressure P at this bigger piston which may be used to lift something very heavy such as a car.
Valves V1 and V2 prevent the back-flow of oil to the small cylinder and the heavy load remains raised up. When the oil stopper is opened, the oil in the large cylinder plows back to the oil tank and the load is brought down.
Brake system in the cars is another common example of a hydraulic system. This consists of a pipe and two cylinders. It is filled with special fluid called brake oil. At one end of the pipe there is a cylinder fitted with a small piston called master cylinder. The small piston is connected with brake pedal. At the other end of the pipe there is a second cylinder fitted with a large piston called slave cylinder. When small piston is pushed into master cylinder by applying a small force on brake pedal, the pressure thus produced is transmitted without loss to the slave cylinder. The large piston in the slave cylinder is pushed out with a large force. It the pushes the brake pad out to make it rub against the moving wheel disc. In this way a large frictional force is produced which stops the running wheel.
Gas pressure in a container
Molecules of a gas in a container are in a continuous state of random motion in all directions. During their motion, they all the time collide with each other and with the walls of the container. Gas molecules colliding with the walls of the container exert force on the walls of the container and thus produce pressure.
If the volume of the container is decreased for the same quantity of gas the distances between the particles also decreases and there are more collisions of the particles with the walls of the container. As a result the gas pressure increases.
The gas pressure can also be increased by adding more gas in the container. Addition of more gas molecules means more collisions with the walls of the container and hence more pressure.