Viscosity
The measure of the resistance of a fluid to flow is known as viscosity. Most fluids have some resistance to motion, the resistance provided by the fluid is called viscosity. This resistance is created by the force of attraction between the fluid molecules. If you pour water through a funnel, it flows easily and quickly, because it has very little resistance. But if you pour honey through a funnel, it may take a little time longer, as the density of honey is high.
Poiseuille's Law
The law of Poiseuille or Poiseuille's equation states that the pressure drop of an incompressible fluid especially a liquid in a laminar flow that passes through a cylindrical tube of length L, radius r, pressure gradient ΔP, and mainly depends on the viscosity of the fluid is nothing but the pressure difference of the layers of fluids. ΔP=P1-P2
Drag Forces
Forces that occur due to the movement of fluid are known as fluid mechanics. Following are the fluids present:
In a water pistol, a piston drives water through a larger tube of radius 1.00 cm into a smaller tube of radius 1.00 mm as in Figure P9.41. (a) If the pistol is fired horizontally at a height of 1.50 m, use ballistics to determine the time it takes water to travel from the nozzle to the ground. (Neglect air resistance and assume atmospheric pressure is 1.00 atm.) (b) If the range of the stream is to be 8.00 m, with what speed must the stream leave the nozzle? (c) Given the areas of the nozzle and cylinder, use the equation of continuity to calculate the speed at which the plunger must be moved.(d) What is the pressure at the nozzle? (e) Use Bernoulli’s equation to find the pressure needed in the larger cylinder. Can gravity terms be neglected? (f ) Calculate the force that must be exerted on the trigger to achieve the desired range. (The force that must be exerted is due to pressure over and above atmospheric pressure.)
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