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
Innate resistance to HIV Innate resistance to HIV A small proportion of humans show partial or apparently complete inborn resistance to HIV, the virus that causes AIDS. The main mechanism is a mutation of the gene encoding CCR5, which acts as a co-receptor for HIV. It is estimated that the proportion of people with some form of resistance to HIV is under 1%. In 1994, Stephen Crohn became the first person discovered to be completely resistant to HIV in all tests performed despite having partners infected by the virus. Crohn's resistance was a result of the absence of a receptor, which prevent the HIV