Question

Velocity of water in a river is
(A) Same everywhere
(B) More in the middle and less near its bank
(C) Less in the middle and more near its bank
(D) Increase from one bank to other bank

Answer 1

Adhesive forces occur due to the result of electrostatic forces which are exerted on different substances. The cohesive forces are associated with van der Waals forces and hydrogen bonding that cause liquid such as water to withstand separation.

Complete step by step solution:
The velocity in the river is more in the middle compared to that near the bank because near the bank there will be sand and dirt particles as a result an adhesive force acts between water particles and these dirt particles which act as frictional force that reduces the velocity of the flowing water. But in the middle of the river there won't be any time these dirt like particles and the velocity will be high in the middle of the river.

Additional Information:
Friction is a kind of resistive force acting between two surfaces in the direction opposite to the motion.
Different types of friction acting on different surfaces are:
1. Static friction
2. Rolling friction
3. Sliding friction
4. Fluid friction

Note:
Adhesion takes place between two different types of molecules or substances. It is mainly caused by electrostatic or mechanical forces that exist among two different kinds of substances.