Test: Fluid Properties - 2 - Civil Engineering (CE) MCQ

Shear Stress (N/m²) = Dynamic Viscosity x Velocity Gradient (1/s) Dimensions of Dynamic Viscocity = M L^-1 T^-1
Velocity Gradient = Velocity(v)/ Distance(y) = m/s-m = 1/s and 1N = kg-m /s²

If for any liquid there, is less attraction for solid molecules or in other words the cohesion predominates, than the liquid will not wet the solid surface and the liquid surface will be depressed at the point of contact with the result the liquid surface is concave downward and the angle of contact ‘θ’ is greater than 90°.

When a droplet is separated initially from the surface of the main body of liquid, then due to surface tension, there is net inward force exerted over the entire surface of the droplet which causes the surface of the droplet to contract from all sides and results in increasing the internal pressure within the droplet the contraction of the droplet continues till the inward force due to the surface tension is in balance with the internal pressure and the droplet forms into sphere which is the shape for minimum surface area..

For thixotrophic fluid, τ = τ₀ + μ (du/dy)ⁿ n < 1
As shear stress τ increases viscosity increases with higher rates of shear strain.

Adhesion- Two different particles binded together-Mixing of milk with water
Cohesion- Two same particles binded together-Mixing of water with water.

Let us suppose that the level of liquid has risen (or fallen) by 'h' above (or below) the general liquid surface when a tube of diameter 'd' is inserted in the liquid. For equilibrium of vertical forces acting on the mass of liquid lying above (or below) the general liquid level, the weight of liquid column ‘h’ (or the total internal pressure in the case of capillary depression) must be balanced by the force, at surface of the liquid, due to surface tension σ. Thus, equating these two forces we have

Ideal fluid are those which have no viscosity and surface tension and are incompressible.

In case of gases the cohesion forces are small and molecular momentum transfer predominates. With the increase in temperature, molecular momentum transfer increases and hence viscosity increases.

The liquid used in manometer should be of high density so as to measure even small variation in pressure.