separated by a distance 'h'. Imagine a cylinder of liquid with axis AB, cross-sectional area A and the liquid in this imaginary cylinder be 'm'. length h. Let the mass of Let P1 and P2 be the pressure at A and B. The forces acting on the cylinder are F1 = P1 A acting vertically downward F2 = P2 A acting upwards on the lower face of the cylinder. Weight (mg) = W of the liquid acting downward. As the liquid is at rest, the net force acting on it should be zero. Note If A and B were at the same height i.e. h=0 then P2 - P1=0 or P1 = P2 i.e., Pressure is same at all points inside a liquid lying on the same horizontal plane. If g = 0 at place, then P2 = P1 at any two points inside the liquid (Pascal's law neglecting effect of gravity). HYDRAULIC MACHINES VISCOSITY : Viscosity is the property of a fluid by virtue of which an internalfrictional force comes into play when the fluid is in motion and opposes the relative motion of its different layers. Viscous drag acting between two layers of liquid each of area moving with velocity F A, gradient is given by h is the coefficient of viscosity of liquid. dv/dx F = A dv/dxwhere η SI unit of is poiseuille of N s m–2 or Pascal-second η
separated by a distance 'h'. Imagine a cylinder of liquid with axis AB, cross-sectional area A and length h. Let the mass of the liquid in this imaginary cylinder be 'm'. Let P1 and P2 be the pressure at A and B. The forces acting on the cylinder are F1 = P1 A acting vertically downward F2 = P2 A acting upwards on the lower face of the cylinder. Weight (mg) = W of the liquid acting downward. As the liquid is at rest, the net force acting on it should be zero. Note If A and B were at the same height i.e. h=0 then P2 - P1=0 or P1 = P2 i.e., Pressure is same at all points inside a liquid lying on the same horizontal plane. If g = 0 at place, then P2 = P1 at any two points inside the liquid (Pascal's law neglecting effect of gravity). HYDRAULIC MACHINES VISCOSITY : Viscosity is the property of a fluid by virtue of which an internalfrictional force comes into play when the fluid is in motion and opposes the relative motion of its different layers. Viscous drag F acting between two layers of liquid each of area A, moving with velocity gradient dv/dx is given by F = η A dv/dxwhere h is the coefficient of viscosity of liquid. SI unit of η is poiseuille of N s m–2 or Pascal-second
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