Physics · Mechanical Properties Of Fluids · NEET
Pressure is transmitted equally, not force. Pascal's law says the added pressure is the same at every point of the enclosed fluid. Since force = pressure x area (F = P A), a piston with a larger area feels a larger force even though the pressure is the same. This is the whole idea behind a hydraulic lift: same pressure, bigger area, bigger output force.
Form 1: In a fluid at rest, the pressure is the same at all points that are at the same height (same depth). Form 2: When external pressure is applied to any part of an enclosed fluid, that pressure change is transmitted undiminished and equally to every point of the fluid and the walls of the container. NCERT states both. Most numerical questions use Form 2 (hydraulic machines).
Yes, it applies to any confined fluid, which includes both liquids and gases at rest. NCERT even uses Pascal's law for gas pressure in the kinetic theory chapter. But hydraulic machines use liquids because liquids are almost incompressible, so the applied pressure passes through fully instead of being wasted on squeezing the fluid smaller.
Because force depends on area. The transmitted pressure P is equal on both pistons, but F = P A. So the small piston with area A1 has force F1 = P A1 and the large piston with area A2 has force F2 = P A2. Dividing gives F2 = F1 x (A2 / A1). A bigger area gives a bigger force. The extra force is not free energy; the small piston must move a much longer distance.
It means the pressure you add does not fade or shrink as it travels through the fluid. If you push and add an extra 200 Pa at one point, every other point of the enclosed fluid also gains exactly 200 Pa (plus whatever depth pressure rho g h it already had). The word undiminished simply means 'without any loss'.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A pressure change applied to an enclosed fluid at rest is transmitted undiminished and equally to every point of the fluid and to the walls of its container.
Blaise Pascal (1623-1662) was a French scientist. The SI unit of pressure, the pascal (Pa), is named in his honour. 1 Pa = 1 N per square metre.
For a hydraulic machine the working relation is P = F1 / A1 = F2 / A2, so F2 = F1 x (A2 / A1). The pressure P is common to both pistons.
Only in a closed container can the added pressure be trapped and passed on to all points. In an open fluid the extra push would just move the fluid or escape, so it would not be transmitted undiminished everywhere.
Hydraulic lift, hydraulic brakes, hydraulic press and the car jack. All use a small force on a small piston to produce a large force on a large piston.
