Fluid Mechanics-I Spring 2010

1. Fluid Mechanics-ISpring 2010 Lecture #03

2. Fluid Statics • The analysis of the action of forces on the fluids at rest are known as Fluid Statics. • Atmosphere around us • Oceans and dams

3. Fluid Forces Depends upon surface area e.g. Pressure Depends upon volume of fluid e.g. gravity

4. Hydrostatic Condition • The fluids at rest has no shear stress. • Only force applied are the normal stresses i.e. pressure. • The variation in pressure of the fluid at rest is only due to the weight of the fluid.

5. Pressure (Static) The normal stress on any plane through a fluid element at rest is a point property, called fluid pressure.

6. Forces on a Fluid Element

7. Assumptions • No Shear stress • Each face has its own pressure. • The element is so small that the pressure on each face is constant. • There is no acceleration of fluid element.

8. Conclusion • There is no change of horizontal pressure. • The change of pressure in vertical direction is only due to density, gravity and height.

9. Pascal’s Law • The intensity of pressure at any point in a fluid at rest is the same in all directions. • The pressure p in a static fluid is a point property independent of orientation.

10. Hydrostatic Condition • Pressure in a static fluid varies only with vertical distance and is independent of the shape of container. • The pressure is the same on a given horizontal plane in the fluid. • Pressure increases with depth in the fluid.

11. Hydrostatic Condition

12. Record of Pressure • Gage pressure (pabs>pa)= pabs-pa • Vacuum pressure (pabs<pa)=pa-pabs

13. Example of Record of Pressure