Name :- Margeel Shah -140410109094 Smarth Shah-140410109095 Smit Shah-140410109096 Rehan Shaikh-140410109097

Subject:-ATHE

Topic :-Fluid Properties Density , Viscosity , Surface tension & Capillarity ….

Capillarity

DEFINITION….Ability of a liquid to flow in narrow spaces without the

assistance of, and in opposition to, external forces like gravity

Capillary action is sometimes called capillarity, capillary motion, or wicking

EXAMPLES….Drawing up of liquids between the hairs of a paint-brush

Drainage of constantly produced tear fluid from the eye

Observed in thin layer chromatography

draws ink to the tips of fountain pen nibs

moving groundwater from wet areas of the soil to dry areas

TYPES…..

Capillarities are of two typesCapillarity rise

Capillarity fall

CAPILLARITY RISETendency of liquids to rise in tubes of small diameter in

opposition to, external forces like gravity

CAPILLARITY FALL

Tendency of liquids to be depressed in tubes of small diameter in opposition to, external forces like gravity

APPLICATIONS… Lubricating oil spread easily on all parts because of their low

surface tension.

Cotton dresses are preferred in summer because cotton dresses have fine pores which act as capillaries for sweat.

Dirt get removed when detergents are added while washing clothes because surface tension of water is reduced.

The absorption of ink by a blotting paper is due to capillary action, as the blotting paper is porous. When it is placed over the ink, the ink raises into the pores. Also rise of oil in the wick of a lamp is due to capillary action.

If one end of a towel is dipped into a bucket of water and the other end hangs over the bucket, the entire towel soon becomes wet due to capillary action.

Supply of water to the leaves at the top of even a tall tree is through capillary rise.

A fabric can be waterproof, by adding suitable waterproofing materials to the fabric. This addition increases the angle of contact, thereby making the fabric waterproof.

FluidsLiquids and gases are both fluids:a fluid is any substance that flows and

takes the shape of its container.

FluidsThe science and technology of the

mechanical properties of liquids is called hydraulics.

Similarly, the science and technology of the mechanical properties of air and other gases is called pneumatics.

CompressibilityGases are therefore highly compressible: their particles can be forced back closer together.

DensityThis means that their density, their mass per

unit volume, is variable.

Density has units of kg/m3.

DmVVDm

VmD

Surface Tension

DefinitionThe net effect is that the molecules at the

surface of the liquid experience an inward force toward the bulk.

Such a force pulls the molecules of the

interface together and, as a result, contracts the surface, resulting in a surface tension.

This “tension” in the surface is the force per unit length that must be applied parallel to the surface so as to counterbalance the net inward pull.

Interfacial tension is the force per unit length existing at the interface between two immiscible liquid phases and.

the surface and interfacial tensions, have the units of dynes/cm or N/m.

Surface Free Energy and Surface TensionThe surface layer of a liquid possesses

additional energy as compared to the bulk liquid.

This energy increases when the surface of the same mass of liquid increases and is therefore called surface free energy.

Viscosity

Velocity Gradient

The resistance tends to keep the fluid in place. Law of inertia

The fluid moves most near the object and least farther away.

This is a velocity gradient.

yvx

yvx

F

Law of Viscosity

Newton combined these two proportionalities.

This is the law of viscosity. A is the area of the solid sliding on

the fluid

The constant h is the dynamic viscosity and depends on the type of fluid.

yvAF xh

yvx

F

Drag Force

Objects falling through a fluid reach terminal velocity.

For low speeds this is due to viscocity.

Stokes’s Law describes the drag force.

rvFd h6

Fg

FbFd

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