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
What It Is to Burn with boiling liquid. Doherty said they "just wanted some cool imagery". The art direction and design were done by P.R. Brown, who also did the photography with Kris McCaddon. Initial pressings of the album contained a demo version of "What It Is to Burn", produced by Chris Fuderich. It was replaced on later pressings with a re-recorded version, produced by Trombino. These later pressings were available from June onwards. The UK edition, released on June 2, included an acoustic version of "Letters to You" and the demo of "What It Is to Burn" as bonus tracks. Following the album's release,