<P> Under most use, a bottle opener functions as a second - class lever: the fulcrum is the far end of the bottle opener, placed on the top of the crown, with the output at the near end of the bottle opener, on the crown edge, between the fulcrum and the hand: in these cases, one pushes up on the lever . </P> <P> However, one may instead use it as a first - class lever, by placing the near end on the top of the crown, and the far end under the crown edge, then pushing down on the lever (thus the output is on the opposite side of the fulcrum from the hand). This is particularly used with bar blades, which form an obtuse angle . Mechanically, this is a marginally less effective lever, as the effort arm is shorter, but the action of pushing down is marginally anatomically easier . </P> <P> While most lever - type bottle openers can be used in either configuration, the designed use can be determined if one of the edges is curved, in which case this edge is designed to sit in the middle of the crown, as the curve concentrates pressure, deforming the crown, and a curved edge does not connect with as much of the crown edge, hence being suboptimal and slipping more frequently if used to connect with the crown edge . This difference can be seen in comparing the traditional opener and contemporary bar blade at right . </P> <P> This common wine opener consists of a flat housing (often plastic covered) similar to a Swiss army knife with a corkscrew and lever (which doubles as crown cork opener) with either a knife or auto - foiler to remove the foil top of wine bottles and then the cork . Designed to be screwed in to within 1 full rotation before the end of the screw (more will pierce the bottom of the cork and result in extra flotsam on the surface of your wine) before levering out the cork . </P>

What kind of simple machine is a wine opener