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Mechanical Properties of Fluids

Explain why?
(b) Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)

Mercury molecules, which make an obtuse angle with glass have a strong force of attraction between themselves and a weak force of attraction toward solids. Hence, they tend to form drops.

On the other hand, water molecules make acute angles with glass. They have a weak force of attraction between themselves and a strong force of attraction toward solids. Hence, they tend to spread out.

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Explain why

(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.

The angle between the tangent to the liquid surface at the point of contact and the surface inside the liquid is called the angle of contact (θ).

At the line of contact, the surface forces between the three media must be in equilibrium.

i.e., cos θ = (S_sa - S_la) / S_lawhere,

s_lais the liquid-air interface,
S_sa is the solid-air interface

The angle of contact θ , is obtuse if S_sa < S_la (as in the case of mercury on glass). This angle is acute if S_sl < S_la (as in the case of water on glass).

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Explain why:
(d) Water with detergent dissolved in it should have small angles of contact.

Water with detergent dissolved in it has small angles of contact (θ). This is because for a small θ, there is a fast capillary rise of the detergent in the cloth. The capillary rise of a liquid is directly proportional to the cosine of the angle of contact (θ). If θ is small, then cosθ will be large and the rise of the detergent water in the cloth will be fast.

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Expalin why?
(c) Surface tension of a liquid is independent of the area of the surface

Surface tension is the force acting per unit length at the interface between the plane of a liquid and any other surface. This force is independent of the area of the liquid surface. Hence, surface tension is also independent of the area of the liquid surface.

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Explain why:
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than 100 km.

Near the sea level, density of air is the maximum. With increase in height from the surface, density of air decreases. At a height of about 6 km, density decreases to nearly half of its value at the sea level. Atmospheric pressure is proportional to density. Hence, at a height of 6 km from the surface, it decreases to nearly half of its value at the sea level.

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Mechanical Properties of Fluids

Explain why:
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than 100 km.

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Mechanical Properties of Fluids

Explain why:(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than 100 km.

Explain why:
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than 100 km.