Class 11PhysicsFluid Mechanics and Surface TensionBasic of Surface tenstion , Adhesive force and Cohesive force
EasyShow that the force exerted by a fluid at rest is perpendicular to its contact surface.
(N/A) Consider an object submerged in a fluid at rest. The fluid exerts a force on the surface of the object. This force must be normal (perpendicular) to the surface.
To prove this by contradiction,assume that the force exerted by the fluid has a component parallel to the surface. According to $Newton's$ third law,the object would exert an equal and opposite force on the fluid parallel to the surface.
Since the fluid is at rest,it cannot sustain a shear stress (a force parallel to the surface). If such a parallel force existed,it would cause the fluid particles to flow along the surface. However,since the fluid is in a state of rest,no such flow occurs.
Therefore,the force exerted by the fluid at rest must be strictly perpendicular to the surface in contact with it.
To prove this by contradiction,assume that the force exerted by the fluid has a component parallel to the surface. According to $Newton's$ third law,the object would exert an equal and opposite force on the fluid parallel to the surface.
Since the fluid is at rest,it cannot sustain a shear stress (a force parallel to the surface). If such a parallel force existed,it would cause the fluid particles to flow along the surface. However,since the fluid is in a state of rest,no such flow occurs.
Therefore,the force exerted by the fluid at rest must be strictly perpendicular to the surface in contact with it.
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Similar Questions
If for a liquid in a glass vessel,the force of cohesion $(F_C)$ is twice the force of adhesion $(F_A)$,then which of the following statements are correct?
$(A)$ The meniscus will be convex.
$(B)$ The liquid will wet the glass.
$(C)$ The angle of contact will be obtuse.
$(D)$ There will be capillary descent in a glass capillary dipped in the liquid.
Correct option$(s)$ is/are:
$(A)$ The meniscus will be convex.
$(B)$ The liquid will wet the glass.
$(C)$ The angle of contact will be obtuse.
$(D)$ There will be capillary descent in a glass capillary dipped in the liquid.
Correct option$(s)$ is/are:
Medium
View SolutionWhen drops of mercury are placed on a clean surface of glass,they merge and become a single drop. Explain.
Easy
View SolutionIn a sphere of influence,the liquid molecule at its centre is
Explain why:
$(a)$ The angle of contact of mercury with glass is obtuse,while that of water with glass is acute.
$(b)$ 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.)
$(c)$ Surface tension of a liquid is independent of the area of the surface.
$(d)$ Water with detergent dissolved in it should have small angles of contact.
$(e)$ $A$ drop of liquid under no external forces is always spherical in shape.
$(a)$ The angle of contact of mercury with glass is obtuse,while that of water with glass is acute.
$(b)$ 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.)
$(c)$ Surface tension of a liquid is independent of the area of the surface.
$(d)$ Water with detergent dissolved in it should have small angles of contact.
$(e)$ $A$ drop of liquid under no external forces is always spherical in shape.
Medium
View SolutionIn a glass capillary tube,the shape of the surface of the liquid depends upon:
Easy
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