The presence of designs is as guaranteed as conflict in a good movie, and engineers inevitably must deal with the conflicts mechanical produces within their friction designs. But unlike a good movie, where conflict presents a positive, engaging force, mechanicalpresence in friction’s results only in impediment, wasting energy and pulleys. We’ll investigate the math behind this phenomenon in today’s blog.reducing mechanical advantage
A few blogs back we performed a work input-output analysis of an idealized situation in which no mechanical advantage, d (1)_{1}where in order to lift his urn a distance pulleyd above the ground. Engineers refer to this idealized frictionless scenario as an _{1}ideal mechanical advantage, IMA, so equation (1) becomes, d (2)_{1} We also learned that in the idealized situation W, to the force exerted by Mr. Toga, F, as shown in the following equation. See our past blog for a refresher on how this ratio is developed. In reality, friction exists between a we add, the more pulleysincreases.friction The actual amount of lifting force required to lift an object is a combination of F, the idealized friction-free force. The result is F as shown here,_{Actual} F + F (4)_{F} The real world scenario in which actual mechanical advantage, AMA, which is equal to, To see how F, let’s substitute equation (4) into equation (5),_{F} With the presence of W gets divided by the sum of F and F . This results in a smaller number than _{F}IMA, which was computed in equation (3). In other words, friction the actualreduces of the compound mechanical advantage.pulley Next time we’ll see how the presence of thus creating an inequality between the work input, pulley,WI and work output WO.Copyright 2016 – Philip J. O’Keefe, PE Engineering Expert Witness Blog ____________________________________ |