# When can viscous forces be neglected?

## When can viscous forces be neglected?

Solid boundaries In turbulent flow regimes (Re >> 1), viscosity can typically be neglected, however this is only valid at distances far from solid interfaces.

Why do we prefer to measure relative viscosity of a liquid compared to absolute viscosity?

Relative viscosity: Relative viscosity is important for non-Newtonian fluids, specifically polymers. It refers to the relationship between molar mass (the mass of a chemical compound divided by total amount) and viscosity — higher molar mass means higher viscosity in the polymer.

Under what conditions viscous effects are negligible in flows?

Viscous forces are negligible compared with inertial forces when the Reynolds number is large. For the flow around an airfoil, this conclusion is nearly correct except that it leads to important contradictions with physics.

### Why viscosity in gases does not depend on pressure?

On increasing pressure viscosity of liquid molecules increases due to the increase in the resistance to the flow of liquid. On increasing pressure, the viscosity of gas molecules decreases due to the increase in glow of molecules. Under most conditions, viscosity is independent of pressure.

Which forces are neglected to obtain Ulysse equation of motion from Newton’s second law?

Explanation: Viscous force, Turbulence force, Compressible forces are neglected to obtain Euler’s equation of motion from Newton’s second law of motion.

Why is the viscous force the relative motion between the adjacent layers of a fluid in motion always opposed?

Explanation: According to the No-Slip condition, the relative velocity between the plate and the fluid in contact with it must be zero. Explanation: Viscosity is the internal friction of a fluid in motion. It is the property by the virtue of which the relative motion between two adjacent fluid layers is opposed. 3.

## Why is it important to know the viscosity of a liquid?

Viscosity of a liquid is an important parameter as it can be used as an indicator of quality by the consumer, in some instances a thicker liquid being thought of as superior quality when compared to a thinner product. Viscosity is also a characteristic of the texture of food.

What is meant by relative viscosity?

Relative Viscosity (ηrel) Definition: The ratio of the viscosities of the polymer. solution (of stated concentration) and of the pure. solvent at the same temperature. Also known as SOLUTION. SOLVENT VISCOSITY RATIO.

Why is viscous force non conservative?

Viscous force is somewhat like friction as it opposes, the motion and is non-conservative but not exactly so because. b) It is velocity independent while friction is not. c) It is temperature dependent while friction is not. d) It is independent of area like surface tension while friction is dependent.

### Which is the correct interpretation of Newton’s law of viscosity?

Equation (3.1.3) is called the Newton’s law of viscosityand states that the shear stress between adjacent fluid layers is proportional to the negative value of the velocity gradient between the two layers. An alternative interpretation can be given to (3.1.3) by noting, from elementary physics, that

How is the drag force related to viscosity?

Viscosity and drag Drag force arises when an object moves through a ﬂuid or, equivalently, when ﬂuid ﬂows past an object. In general, the drag force grows larger with increased ﬂow velocity, but viscosity is a complex phenomenon that cannot be reduced to the simple relationship “drag force is proportional to velocity”.

How is viscosity expressed in the SI system?

In the SI system, viscosity is expressed in kg m-1 s-1; however, sometimes viscosity values are shown in terms of the equivalent units of N m-2 s or Pa s, where the Pascal (Pa) is the SI unit of pressure and is equal to 1 Newton per square meter (Table A-1). The SI unit of viscosity is equal to 10 Poise or 1000 centipoise.

## Which is the unit of viscosity in the metric system?

By substituting the dimensions of force, area, length and velocity in (3.1.3) we find that the dimensions of viscosity are M L-1 t-1. In the metric system, the unit of viscosity is the Poise (1 P = 1 g cm-1 s-1), which is subdivided to 100 centipoise (cP).