fluid 11.pptx | physics fluid the science hub

fluid

1. FLUID PRESSURE

2. FLUID PRESSURE EFFECTIVE FORCE ON A BODY FALLING IN ALIQUID : STOKES LAW Viscous force limit the speed of body falling in a liquid F = 6 πη rv

3. FLUID PRESSURE Importance of Stoke’s Law Millikan employs this rule in his oil-drop experiment to determine the electric charge . Working of a parachute is based on the principle of Stoke’s Law. Cloud formation and floating are explained using Stoke’s Law.

4. FLUID PRESSURE v = 2r2 × (ρ−σ)g / 9η where ρ is the mass density of the sphere σ is the mass densities of the fluid r is the radius of the raindrop Terminal velocity The maximum constant velocity acquired by a body while falling through a viscous medium is called its Terminal Velocity.

5. FLUID PRESSURE Conditions for Stoke’s Law Conditions under which Stoke’s Law is valid are, The fluid through which the body moves must have an infinite extension. The body is perfectly rigid and smooth. There is no slip between the body and the fluid. The motion of the body does not give rise to turbulent motion. Hence, the motion is streamlined. The size of the body is small, but it is larger than the distance between the molecules of the liquid. Thus, the medium is homogeneous and continuous for such a body.

6. FLUID PRESSURE Applications of Stoke’s Law Velocity of Raindrops Parachute When we jump out of an aeroplane , a parachute assists us in landing safely on the ground Terminal Velocity When a body falls through a viscous fluid, it produces relative motion between its different layers.

7. Limitations of the Stoke’s Law FLUID PRESSURE Stokes’ equation is invalid if the  density  difference in the equation is negative When the solid content of a  suspension  is high, Stokes’ equation may not show the real sedimentation rate. High solid content imparts additional viscosity to the system, The equation contains only the viscosity of the medium Dielectric Constant Brownian Movement Another aspect that can affect the precision of Stokes’ equation results is  Brownian movement , which is a spontaneous (zigzag) movement of particles floating in a fluid caused by collisions with fast-moving atoms or molecules in the gas or liquid. Sedimentation is mitigated to some degree by Brownian migration .

8. FLUID PRESSURE 1: A raindrop of radius 0.3 mm falls through the air with a terminal velocity of 1 m/s. The viscosity of air is 18 × 10-5 Poise. Find the viscous force on the raindrop.

9. FLUID PRESSURE 2: A solid metal ball falling in a liquid column attains a terminal velocity of 3 m/s. Find the viscosity of the liquid if the radius of the ball is r = 7 cm and its density is dl = 1000kg/m3 and the density of the metal ball is ds = 7050 kg/m3 (Take g = 10 m/s2)

10. Viscosity and Laminar Flow; Poiseuille’s Law FLUID PRESSURE Layers flow without mixing when flow is laminar