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Home > News & Articles > Mechanical Properties of Fluids: Definition, Pascal's Law, Pressure and Law of Floatation
Updated on 20th April, 2023 , 10 min read
A substance that starts to flow when an external force is applied is referred to as a "fluid." Fluids have distinctive physical characteristics that control how they respond to applied forces.
Hydrostatics is the study of a fluid's mechanical characteristics. A substance that gives in to even the smallest pressure is said to be fluid.
Fluids can be categorized into two groups: liquids and elastic fluids or gases, which later include the atmosphere's air and all the other types of air that chemistry has introduced us to. We will focus only on the mechanical characteristics of liquids or non-elastic fluids at this time.
When compared to solid objects, fluids exhibit the gravitational effects more accurately due to the strong cohesive attraction of the latter's particle population, which partially offsets the gravitational pull of gravity.
The normal force acting per unit area is defined as fluid pressure, or p, at each point. Mathematically,
p = dFl
—-
dA
The S.I. unit of pressure is the pascal (Pa) and 1 pascal=1N/m²
Regardless of how the surface is oriented, fluid force acts perpendicularly to that surface. As a result, fluid pressure can be thought of as a scalar quantity because it lacks an inherent direction of its own.
If the weight of the liquid displaced by the portion of the body that is submerged is equal to the weight of the body, the body floats. The various forces acting on a body when it is partially or completely submerged in a liquid are
(i)upward thrust (T) acting at the centre of buoyancy and whose magnitude is equal to the weight of the liquid displaced and
(ii)the weight of the body (W), which acts vertically downward through its center of gravity.
(a) The body sinks in the liquid when W > T;
(b) The body will continue to be in equilibrium inside the liquid when W = T;
(c) If W < T, the body will rise to the liquid's surface in such a way that the weight of the body plus the weight of the liquid is displaced by its immersed portion. As a result, only a portion of the body will be submerged in the liquid, causing it to float.
—- = const
2
Viscosity is a property of a fluid that prevents relative motion between its various layers, and the force that results from this property is known as the viscous force. Mathematically, viscous force is given by:
F= −ηA dv
—-
dx
Where, η is a constant dependent on the nature of the liquid and is termed the coefficient of viscosity and
dv is the velocity gradient.
—-
dx
Pa.s or Nsm-² is the S.I. unit of coefficient of viscosity.
CGS unit of viscosity is poise(1Pa.s=10 poise).
In a free fall through a viscous medium, it describes the highest constant velocity a body can achieve. Mathematically,
vr= 2r²(ρ− ρ₀)g
—-----------
9η
In capillary tubes, Poiseuille discovered the liquid's stream-line flow. The volume of liquid leaving the tube each second is equal to
πPr⁴
-—--.
8ηl
1. Viscosity forces help to maintain the stability of laminar flow. However, it is evident that when the flow rate is high, laminar or steady flow is disrupted. High flow rates result in turbulence, which is an irregular, unsteady motion.
2. Reynold's number is a dimensionless number whose value gives a rough idea of the flow rate and whether or not it will be turbulent. Mathematically, it is given by
Re= ρvD
—---.
η
where ρ is the density of the fluid flowing at speed v, D is the diameter of the tube, and η= the coefficient of viscosity of the fluid.
3. When Re is less than 1000, the flow is observed to be streamline or laminar, whereas when Re > 2000, the flow is turbulent. Additionally, between 1000 and 2000, the flow for Re becomes erratic.
1. The force per unit length in the plane of a liquid surface perpendicular to either side of a fictitious line drawn on that surface is referred to as the surface tension of a liquid. Mathematically,
S = F
—, where S is the surface tension of a liquid.
l
2. Unit of surface tension in MKS system: N/m or J/m².Unit of surface tension in CGS system: dyne/cm or erg/cm².
Work must be done over the liquid's surface in order to increase surface area. The potential energy of this work is stored in the liquid surface. Therefore, the excess potential energy per unit area of a liquid's surface is referred to as the liquid's surface energy. Mathematically, W= SΔA; where ΔA= increase in surface area.
This theorem states that the velocity of efflux, or the speed at which liquid exits an orifice (a small hole), is equivalent to the speed that a body falling freely would reach after falling through a vertical distance equal to the orifice's depth below the liquid's free surface.
The velocity is determined by
V = √2gh
A ball will follow a curved path that is convex toward the side of greater pressure when it is spun while it is in a streamline of air molecules. The ball getting a lift and areodynamics from spin bowlers are based on this theory.
A very narrow glass tube with a fine borehole and open at both ends is called a capillary tube. When a capillary tube is dipped in a liquid, the liquid will rise or fall in the tube, and this reaction is known as capillarity.
Mathematically, capillary rise or fall (h) is given by
2Scosθ 2S
h = —----- = —-----
Rρg Rρg
Where,
S= surface tension
θ= angle of contact
r= radius of capillary tube
R= radius of meniscus
ρ= density of liquid
A capillary tube can be referred to as having "insufficient length" if its length is less than the height to which a liquid would actually rise in it (h).
In this instance, liquid ascends to the top of the l(l
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readAns. The thermodynamic characteristics of fluids are their temperature, density, pressure, and specific enthalpy. Physical characteristics: These characteristics, such as color and odor, aid in understanding the fluid’s physical state.
Ans. Unit: Mechanical properties of fluid, Density and pressure, Buoyant force and Archimedes’ principle, Fluid dynamics,Viscosity, Surface tension.
Ans. One of the states of matter is a fluid, which we define as liquids, gases, or plasma.
Ans: Density, viscosity, surface tension, capillarity, specific volume, and specific weight are the fundamental characteristics of fluids.
Ans. A fluid’s viscosity is a measurement of how resistant it is to deformation at a specific rate. It is equivalent to the colloquial term "thickness" for liquids.
The main mechanical properties of fluids are viscosity, density, surface tension, compressibility, and bulk modulus. These properties describe how fluids behave when subjected to mechanical forces, such as stress, strain, and pressure.
Viscosity is a measure of a fluid’s resistance to flow. Higher viscosity fluids flow more slowly than lower viscosity fluids. Viscosity is an important factor in many industrial applications, such as lubrication, pumping, and mixing.
Surface tension is the property of a fluid that causes its surface to behave like a stretched elastic membrane. This property arises from the cohesive forces between the fluid molecules at the surface. Surface tension can affect fluid behavior by causing liquids to form droplets, allowing insects to walk on water, and creating capillary action.
Compressibility is the measure of a fluid’s ability to change its volume in response to changes in pressure. It is an important property in the study of fluid mechanics, as it affects the propagation of sound waves through fluids and the performance of compressors and turbines.
The bulk modulus is a measure of a fluid’s resistance to changes in volume under pressure. It is important in the study of fluid mechanics because it affects the transmission of pressure waves through fluids. High bulk modulus fluids are better at transmitting pressure waves than low bulk modulus fluids, making them useful in applications such as hydraulic systems and shock absorbers.
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