Friction friction and wear in so-called self-lubricating materials. Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is named "viscosity". In everyday terms, the viscosity of a fluid is described as its "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. The less viscous the fluid, the greater its ease of deformation or movement. All real fluids (except superfluids) offer some resistance to shearing and therefore are viscous. For teaching and explanatory purposes it is helpful to use the concept of an inviscid fluid
Resistance artery Resistance artery A resistance artery is small diameter blood vessel in the microcirculation that contributes significantly to the creation of the resistance to flow and regulation of blood flow. Resistance arteries are usually arterioles or end-points of arteries. Having thick muscular walls and narrow lumen they contribute the most to the resistance to blood flow. Degree of the contraction of muscles in the wall of a resistance artery is directly connected to the size of the lumen. Functionally from physiological point of view blood vessels can be divided in several categories Particular feature of resistance vessels is ability to change