1. P3.2.3 Hydraulics and Pressure A hydraulic system uses pressure in a liquid to transfer force from one place to another to do mechanical work. You must assume that a)The liquid is INCOMPRESSIBLE : it is not elastic: you can’t squash it. b)Pressure acts in all directions within the liquid (Note: similar systems use air pressure: they are described as PNEUMATIC but air is compressible) ‘Candidates should understand that this means that a force exerted at one point on a liquid will be transmitted to other points in the liquid.’ The pressure in different parts of a hydraulic system is given by: Pressure = Force or P = F/A Area P is measured in Pascals (Pa), F is the force in Newtons, N A is the cross-sectional area in metres squared, m 2

2. P3.2.3 Hydraulics Simple examples of the pressure idea include the difference in pressure when the SAME FORCE is applied through different AREAS. Try these examples yourself (you may need a calculator): 1) An office safe has a weight of 500N. If the area of the base is 1.25 square metres, what is the pressure on the floor of the office? 2) A physics teacher has a weight of 800N. If his feet have an area of 0.025 square metres each, what pressure does he exert on the ground? (Remember, he has two feet!)

3. P3.2.3 Hydraulics The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier. Example calculation: If the FORCE IN is 20N and the area of cylinder A is 0.02m 2 then the PRESSURE in the HYDRAULIC LIQUID is P = F/A = 20/0.02 = 1000 Pa The pressure all the way to cylinder B is THE SAME. If the area of cylinder B is 0.08m 2 then the FORCE OUT = P x A = 1000 x 0.08 = 80N So the system has multiplied the force by a factor of 4

4. P3.2.3 Hydraulics The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier. This principle is used in the braking systems of vehicles. http://www.darvill.clara.net/enforcemot/pressure.htm

5. P3.2.3 Hydraulics Hydraulic disc brakes use the pressure of the fluid (light blue) to push a piston towards the brake rotor. The piston pushes brake pads onto the disc so friction acts between the pads and the rotor or disc. http://www.darvill.clara.net/enforcemot/pressure.htm

6. P3.2.3 Hydraulics The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier. http://www.darvill.clara.net/enforcemot/pressure.htm On a disk brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in-turn, squeezes two brake pads against the disk (rotor), which is attached to the wheel, forcing it to slow down or stop.disk brakerotor This process is similar to a bicycle brake where two rubber pads rub against the wheel rim creating friction.

7. P3.2.3 Hydraulics The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier. http://www.darvill.clara.net/enforcemot/pressure.htm

8. P3.2.3 Hydraulics The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier. http://www.darvill.clara.net/enforcemot/pressure.htm