In a simple fixed pulley (Fig - 1), one end of the rope passing over the grooved disc is tied to the weight being lifted while its other end is free to be pulled down, thereby making an effort to lift the weight. An ideal rope and pulley system simplifies the work done in pulling the rope and lifting the load against the gravitational pull. It does this by the transmission of linear motive force of the pull at end, through the entire rope to the lifted load at the other end. There is no net force acting on the pulley system at equilibrium as the force on the pulley axle is equally distributed along the two arms of the rope passing through the pulley. When the system is in action, the energy conservation principle is followed, with the work done in lifting the load (weight times the distance through which it is lifted) is equal to the tension in the rope or in other words the force with which the load is lifted. Lesser the magnitude of the lifting force compared to the weight of the lifted load greater is the mechanical advantage (MA) of pulleys, which is the ratio of the lifted weight to the force exerted for lifting. The most novel thing about pulleys is that they reverse the direction of the force, thereby minimizing the effort. Pulling something downward is easier being assisted by gravity. So, by tugging at the rope downward, the weight tied to the other end of the rope is easily lifted through the air by a simple fixed pulley. (Walker, 12) The second most fascinating aspect about pulleys is the force by which the load is being pulled is equal to the tension along each rope line. Hence, greater number of ropes makes weight lifting easier and effortless for pulleys as the net weight is divided among the total number of ropes running through the pulley. Adding multiple pulleys increases the number of rope lines for distributing the total lifted weight among them (Fig - 3), thereby increasing the mechanical advantage. (Mezzanotte, 14)
MATERIALS AND METHODS:
We categorized the pulley system into three types; the single fixed pulley, the single moveable pulley and the combined system of pulleys. We devised one sample of a fixed and a moveable single pulley and four compound pulley systems combining a fixed and a moveable pulley by ropes wound around them in different directions. (Figures - 1 to 7) In each case a weight (W) of 500 grams was tied to the end of the ropes passing over the disc grooves.
First the lifting forces were compared for the fixed and the moveable single rope and pulley systems (Figures - 1 & 2) and the data was collected to be analyzed. The next level of comparison was extended for the compound pulleys (Figures - 3 to 7) and the collected data was correlated with the first set.
The results for the single fixed and moveable pulley system are tabulated below:
Weight equivalent to the exerted force