Simple Machine (Pulley)

Fig. 1

        Pulley is a simple machine made up of wheel and rope. The rope fits into the wheel and one end of the rope is connected to the load. When one end of the rope is pulled, the wheel turned so thus the load. In the diagram, (Fig. 1) a man is pulling one end of the rope to lift the load upward. The Actual Mechanical Advantage (AMA) of a machine can be computed by the formula:

                        AMA= Fo/Fi

wherein Fo is the output force and Fi is the input force or the force that you exert. The IMA or the Ideal Mechanical Advantage could be computed by the formula:
                       IMA= Si/So  
wherein Si is the input distance and So is the output distance. Efficiency(e)= AMA/IMA and no machine can have a 100% efficiency.

            This simple machine (pulley) makes work easier and effortless. Pulley really saves a lot of effort or energy when you have more than one pulley working together.(Fig. 2) It is designed to reduce the amount of force needed to lift a load. Pulleys are used in our everyday life, from vehicles to moving equipments such as of anchors in ships, etc.

 

About the Pulley

       Pulleys are wheels on an axle that have a groove around their outer edge on which a rope or belt can fit. The wheel is designed in such a way to support the movement of the cable or belt that fit along the circumference of the wheel. The application of pulleys can be for many different functions; lifting loads, applying forces or transmitting power. For simple, single fixed pulleys, the load is attached to one end of the rope while the wheel is secured at a higher position with the rope running through it and the force being applied to one end of the rope to lift the load on the other end. This is one of the simplest models of a pulley system demonstrating how it works. There are several different, more complex models of pulley systems that work in different ways to serve different functions.

    
      The wheel can be secured at the top in some pulley systems and can be movable in some. It is easier to lift a load when the wheel is secured at the top and the rope is pulled downwards to lift the load rather than having to pull the rope upwards to lift a load in some movable pulley systems. The output force or work done by a pulley system can be calculated by multiplying the effort required to pull the rope to lift a load with the distance the that the rope moves. Some pulley systems can make use of more than one or more pulleys which are linked. The advantage of using such systems is that they reduce the amount of effort required to get work done.






TYPES OF PULLEY

Fig.2

           

•         The simplest type of pulleys is the fixed pulley systems. These pulleys are the only pulley systems though which, if used individually, require an equal amount of effort to the load to lift it off the ground. In this system, the wheel is secured at a fixed place and does not move. What this system does is that it changes the direction of the force in order to complete a task. The advantage with this is that one does not have to push or pull a load to be able to move the load as it allows for easy displacement of the load. The disadvantage being that more effort is required to move the load as compared to other pulley systems.

•             Unlike a fixed pulley system, in the movable pulley systems, the wheel used in the pulley moves along with the load that is being displaced. This function of the pulleys allows it to use lesser effort to be able to move the load. Unlike fixed pulley systems that exert only as much force on the load as that of which is applied on the rope, movable pulley systems are able to multiply the force that a user applies to the machine to carry out a task, in turn making the job seem more easier. This way, lesser force is required by the user to carry out the same task if using a fixed pulley system. This pulley also acts as a second class lever, whereby the load is placed in between the fulcrum and the effort. The disadvantage with these systems is that one has to pull or push to displace a load and the main advantage is that it requires lesser effort to be able to move the load.

•              The third type of pulley systems present today are the compound pulley systems. These are a combination of fixed and movable pulleys. These systems have the advantages of both the fixed and movable pulley systems as one would not require pushing or pulling a load to be able to move it while using only minimal force. Several pulleys can be combined to make this system. The more pulleys that are used, the lesser the force required to move the load. However, these systems can take up a lot of space and they involve the object moving over a longer distance.