Thursday, September 30, 2010

[Physics Form 4] Pascal's Principle

Look at the following diagrams for a better understanding of Pascal's Principle.

Force Over Area

The symbols F and P represent force and pressure, respectively.

When the force F is exerted on the lower pistons in all four diagrams, it generates a pressure of P0 . The same pressure is generated on the upper pistons in diagrams I, II and III, but not in diagram IV.

In the diagram I and II, the force exerted by the upper pistons are equal to F, whereas in diagram III, the force is bigger than F, and in diagram IV, no force is exerted.

Based on the observations above, some conclusions can be made.

Conclusion (i):
Liquid X can transmit an equal magnitude of pressure from the lower piston to the upper piston. This abides by the Pascal's principle, which states that liquids are able to transmit pressure in equal magnitude in all directions. Air, with the exception of compressed air, however, is unable to transmit pressure.

Conclusion (ii):
Though the pressure generated is the same, the force exerted by the upper piston in diagram III is larger than F. This suggests that a larger surface area of an upper piston is able to multiply the force exerted by a lower piston. Hence, the force exerted is directly proportional to the surface area (the pressure generated on both pistons in diagram III is the same). This application is used in hydraulic brake and jack systems, in which their surface areas are increased to multiply the force exerted by the second piston.

Conclusion (iii):
Pressure on the first piston = pressure on the second piston.

F1 /A1 = F2 /A2

When the Pascal's principle is applied on a hydraulic lift, a force exerted on 'a' can lift a car at 'b'.


Nota Terkini