Question

When water flows through a pipe, which layer moves faster?

Answer 1

Hint: Imagine water is flowing through a pipe. Water has many layers when it is flowing, there is a top layer then the layer beneath the top layer, then the middle layer, etc. As we know that there is friction between any two surfaces, here also there is friction between the two surfaces.

Complete solution:
The top layer of the water and the bottom layer of the water is in contact with the pipe, the friction between the top and bottom layer of the water would be in direct contact with each other and the other deeper layer of the water would be in direct contact with the layers of water. Just like there is frictional force between the two surfaces, there is viscous force between water and the solid surface of the pipe. In other words viscous force is a force between a solid body and a fluid. Its direction is opposite to the direction of the flow of the liquid.
The top layer of water will experience maximum viscous force and the layer beneath the top layer the viscous force will recede. So, due to the viscous force between the top layer of the water and the surface of the pipe the top layer of the water will move the slowest and the layer which is at the centre of the water will move the fastest.

Final answer is, When water flows through the pipe the centre layer of water will move the fastest.

Note: Here, we need to explain about the force that is acting between the pipe and between the water and its relation with frictional force, also explain about the layers that form when flowing through the pipe.