In general, the angle of repose ranges from 0° to 90°; while for sand, it ranges from 30° to 35° [28,29], as reported in Table 2 [30]. Table 2. Typical values of angle of repose [30].

At the end of the avalanche, a new slope forms at a lower angle. The corresponding slope angle is referred to as the dynamic angle of repose. At this stage, grains move continuously from the upper to lower end of the slope, yielding a surface shear layer of grains that flow down the plane inclined at a fixed angle.

There is a minimum angle or maximum slope the sand will maintain due to the forces of gravity and the effect of friction between the particles of sand. The angle of repose for dry sand has been calculated to be 35 degrees, whereas cement has an angle of repose of 20 degrees.

3.3. This angle is called the angle of repose of the material. The angle of repose is important for the design of processing, storage, and conveying systems of particulate materials. When the grains are smooth and rounded, the angle of repose is low. For very fine and sticky materials the angle of repose is high.

Fixed funnel method Stop pouring the material when the pile reaches a predetermined height or the base a predetermined width. Rather than attempt to measure the angle of the resulting cone directly, divide the height by half the width of the base of the cone. The inverse tangent of this ratio is the angle of repose.

The dynamic contact angle is the contact angle which occurs in the course of wetting (advancing angle) or de-wetting (receding angle) of a solid.

The static contact angle is the contact angle with which the contact area between liquid and solid is not changed from the outside during the measurement, in contrast to the dynamic contact angle which is produced in the course of wetting (advancing angle) or de-wetting (receding angle).

Dynamic contact angles can be measured by using Sigma force tensiometer. Force tensiometer measures the mass affecting to the balance when a sample of solid is brought in contact with a test liquid.

In the static method a drop is deposited on a surface and the contact angle can be measured by looking at the drop through a goniometer (an instrument that measures contact angles). The dynamic method is similar to the static one but the drop of liquid which is deposited on a surface is modified.

Contact angle is a measure of wettability Water contact angle will immediately give an indication of the wettability of the solid. If the measured contact angle is above 90 degrees, the solid is said to have poor wetting and is termed hydrophobic. If the contact angle is below 90 degrees, a term hydrophilic is used.

physics. : the angle between the meniscus and the containing walls of a column of liquid measured from the vertical wall below the surface of the liquid to the position of the tangent to the meniscus at its point of contact with the wall.

The angle of contact depends upon the liquid’s nature and the solid in contact and the medium which exists above the free surface of the liquid. The angle of contact increases with an increase in the temperature of the liquid.

The angle of contact does not depend on the pressure of the liquid.

Surface tension generally decreases on increasing the temperature i.e adhesion increases. Hence, angle of contact will increase. In case of impurities, when a highly soluble impurity like NaCl is added to water, surface tension increases whereas it decreases for sparingly solube (eg: phenol) or insoluble impurities.

Apparently this angle is the contact angle. Contact angle and the wetting behavior of solid particles are influenced by many physical and chemical factors such as surface roughness and heterogeneity as well as particle shape and size.

Characteristics of the Angle of Contact: The angle of contact is constant for a given liquid-solid pair. When the angle of contact between the liquid and a solid surface is small (acute), the liquid is said to wet the surface. If the angle of contact is large the surface is not wetted.

The factors are, given below: The nature of the liquid and the solid which is in contact to form the angle of contact. The medium in which angle of contact is being made. The independence of the angle of contact to which the inclination of solid is inclined to the liquid surface.

Answer: The cohesive force between the molecules of mercury is more than the adhesive force between the molecules of mercury and those of glass. Actually,cohesive force and Adhesive forces are the phenomenon due to the surface tension of a liquid. The angle made by the mercury from the glass surface is always obtuse.

The angle of contact of Mercury with glass is obtuse. ,making cosθ negative and the angle of contact obtuse.

138°

Capillarity is the result of surface, or interfacial, forces. The rise of water in a thin tube inserted in water is caused by forces of attraction between the molecules of water and the glass walls and among the molecules of water themselves. The narrower the bore of the capillary tube, the higher the water rises.

Capillary rise or capillarity is a phenomenon in which liquid spontaneously rises or falls in a narrow space such as a thin tube or in the voids of a porous material. Surface tension is an important factor in the phenomenon of capillarity.

Examples of capillarity in Daily life :

• As pen nib is split at the tip to provide the narrow capillary and the ink is drawn upto the point continuously.
• In oil lamps, the oil is drawn up through the capillary of the wick.
• Clay soils are damped as the water rises quickly to the surface through the capillaries.

The extent of capillary rise in a pore is controlled by: the diameter of the capillary tube, the contact angle between the liquid and the wetted surface, density of the liquid, viscosity of the liquid, surface tension, and whether the surface is hydrophobic.

For this study, the factors used to determine capillary rise are the diameter of the capillary tube (representing the diameter of the pores in a soil), the contact angle between the liquid and the surface to which it adheres, the density of the liquid, the viscosity of the liquid, surface tension, and whether or not …

When a glass tube is immersed in mercury, the level of mercury inside the tube falls below the level in the outer vessel. Examples of capillarity: Blotting paper absorbs ink or water, ink rises in a pen, oil rises in wicks of a lamp.

The rise of a column of liquid within a narrow capillary tube is also because of the surface tension. The formula for capillary rise (h) = 2T/[rρg].

The rise of liquid in tube known as capillary rise while depression of fluid level is known as capillary fall. Capillary depend upon density of liquid, surface tension of liquid and the diameter of the tube.

The formula for capillary rise can be derived by balancing forces on the liquid column. The weight of the liquid (πr2hρg π r 2 h ρ g ) is balanced by the upward force due to surface tension (2πrσcosθ 2 π r σ cos ⁡ ). This formula can also be derived using pressure balance.

When length of tube is less than the height of capillary rise, the liquid molecules on reaching top of the capillary come into contact with horizontal surface of the tube. The surface tension becomes horizontal. There is no vertical force to pull the liquid up and it stops rising.