Drop a cup of water on a plate and drop a cup of oil on another similar plate. You will see an interesting point. In the plate where the water is poured, the water spreads quick along the diameter and if you see the cup, you will notice only negligible amount of water falls on the surface of the emptied cup.
However, the oil spreads gradually along the diameter and if you see the cup, you will notice considerable amount of oil remaining on the top of the emptied cup.The phenomenon explained above tells us that fluids do provide resistance to movement which is also referred to as fluid friction and the quantum of fluid friction depends upon the nature of fluid.
Fluids providing higher fluid resistance are known as high Viscous or in common guys term as greasy.
Such as in solids, fluids too have two kinds of fluid frictions.
Dynamic Friction or Kinetic Friction
Examples of Fluid friction:
Assume there is a wet surface among two thin glass plates, you may find the plates get stuck and the base plate does not drop when you hold only the top plate.
This is because of the fluid friction that over comes the tensile stress (the weight) performing on the bottom plate.
The quantum of fluid friction or the viscosity of blood is linked to the biomedical condition of someone.
When an item is fallen into a fluid, the extent of splash because of the buoyant force of the fluid depends upon the fluid friction of that particular fluid.
You find lighter dust articles move quick on the surface of a moving river. This is because of the high velocity gradient at the top layer of water because of lower dynamic fluid friction at that layer.
A dynamic fluid friction is lower in magnitude then the sliding friction of solids. Because of this some fluids are employed as lubricants among surfaces of sliding or rotating things. The contact surfaces then become two sets of surfaces. Fluid to solid contact and solid to fluid contact. Because the fluid friction is less in every set, the total sliding friction gets reduced.
A Rolling friction is actually a resistive force which opposes the rolling motion of an item. Rolling friction takes place when a round item rolls around a surface.
One can obviously conclude by now that the analysis of rolling friction is restricted to rollers or wheels and the surface where they move. That is, for the identical weight, the circumstance is same whether you place material A or material B on similar wheels and carriage.
Rolling Friction Examples:
When the surface is soft where an object rolls, then there is a plowing action, i.e., the wheels spend some power to clear the path. It results in increase in resistive force, quite simply, increase in over all rolling friction. This case is experienced once you drive a vehicle on dirt surfaces.
When the surface of the rolling item is soft due to the material or other physical consideration, then a surface of the item in contact gets deformed which leads to increase in rolling friction due to addition of sliding friction because of such deformity. This is exactly why you find it hard to drive a bicycle with less air pressure in the wheels.