6: Fluid Statics
- Page ID
- 47039
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- 6.1: Prelude to Fluid Statics
- What exactly is a fluid? Can we understand fluids with the laws already presented, or will new laws emerge from their study? The physical characteristics of static or stationary fluids and some of the laws that govern their behavior are the topics of this chapter.
- 6.2: What Is a Fluid?
- A fluid is a state of matter that yields to sideways or shearing forces. Liquids and gases are both fluids. Fluid statics is the physics of stationary fluids.
- 6.3: Density
- Density, as you will see, is an important characteristic of substances. It is crucial, for example, in determining whether an object sinks or floats in a fluid. Density is the mass per unit volume of a substance or object.
- 6.4: Pressure
- Pressure is the force per unit perpendicular area over which the force is applied. In equation form, pressure is defined as \[F = PA.\] The SI unit of pressure is pascal and \(1 \space Pa = 1 \space N/m^2.\)
- 6.5: Variation of Pressure with Depth in a Fluid
- Pressure is the weight of the fluid \(mg\) divided by the area \(A\) supporting it (the area of the bottom of the container): \[P = \dfrac{mg}{A}.\] Pressure due to the weight of a liquid is given by \[P = h\rho g,\] where \(P\) is the pressure, \(h\) is the height of the liquid, \(\rho\) is the density of the liquid, and \(g\) is the acceleration due to the gravity.
- 6.6: Archimedes’ Principle
- Buoyant force is the net upward force on any object in any fluid. If the buoyant force is greater than the object’s weight, the object will rise to the surface and float. If the buoyant force is less than the object’s weight, the object will sink. If the buoyant force equals the object’s weight, the object will remain suspended at that depth. The buoyant force is always present whether the object floats, sinks, or is suspended in a fluid. Archimedes’ principle states that the buoyant force on an
- 6.7: Cohesion and Adhesion in Liquids - Surface Tension and Capillary Action
- Attractive forces between molecules of the same type are called cohesive forces. Attractive forces between molecules of different types are called adhesive forces. Cohesive forces between molecules cause the surface of a liquid to contract to the smallest possible surface area. This general effect is called surface tension. Capillary action is the tendency of a fluid to be raised or suppressed in a narrow tube, or capillary tube which is due to relative strengths of cohesive and adhesive forces.