open tube manometer Fig . Two pressure measuring devices. Fig . (a) The mercury barometer.
Answer Here h = m and ρ = . × kg m - . From Eq. ( .
), absolute pressure P = P a + ρ gh = . × Pa + . × kg m – × m s – × m = . × Pa ≈ atm Gauge pressure is P − P a = ρ gh = P g P g = .
× kg m – × ms × m = × Pa ≈ atm (c) The pressure outside the submarine is P = P a + ρ gh and the pressure inside it is P a . Hence, the net pressure acting on the window is gauge pressure, P g = ρ gh . Since the area of the window is A = . m , the force acting on it is F = P g A = × Pa × .
m = . × N . . Hydraulic Machines Let us now consider what happens when we change the pressure on a fluid contained in a vessel.
Consider a horizontal cylinder with a piston and three vertical tubes at different points [Fig. . (a)]. The pressure in the horizontal cylinder is indicated by the height of liquid column in the vertical tubes.
It is necessarily the same in all. If we push the piston, the fluid level rises in all the tubes, again reaching the same level in each one of them. law. In these devices, fluids are used for transmitting pressure.
In a hydraulic lift, as shown in Fig. . (b), two pistons are separated by the space filled with a liquid. A piston of small cross-section A is used to exert a force F directly on the liquid.
The pressure P = is transmitted throughout the liquid to the larger cylinder attached with a larger piston of