PULLEY AND COMBINED PULLEYS THAT ARE AND HOW THEY OPERATE LOAD AND EFFORT, ANIMATION WELL EXPLAINED

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PULLEY AND COMBINED PULLEYS THAT ARE AND HOW THEY OPERATE ANIMATION WELL EXPLAINED
Pulley, simple machine used to lift objects. A pulley consists of a grooved wheel or disk within a housing, and a rope or cable threaded around the disk. The disk of the pulley rotates as the rope or cable moves over it. Pulleys are used for lifting by attaching one end of the rope to the object, threading the rope through the pulley (or system of pulleys), and pulling on the other end of the rope.
A single fixed pulley changes the direction of the force applied to the end of the rope. A common example of a pulley can be found at the top of a flagpole. Pulling down on the rope causes the flag to go up because the pulley changes the direction of the force applied to the flag. Multiple pulleys can change both the direction of the applied force and the amount of force, so that less force is needed to lift an object. Construction cranes use multiple pulley systems to reduce the amount of force needed to lift heavy equipment.
The pulley is one of the four simple machines (along with the lever, the wheel and axle, and the inclined plane) used to do work. Work is defined in physics as the result of a force, such as the effort of pulling on a rope, that moves an object across a distance. Pulleys reduce the effort to lift an object by increasing the distance over which the effort is applied.
II WORK AND MECHANICAL ADVANTAGE
To lift any object, a person must do some work. Work is the product of the effort, or force, applied to an object multiplied by the distance the force is applied. The relation of work to force and distance can be show as an equation:
Work = Force × Distance
A pulley makes work easier by increasing the distance over which effort is applied. Pulleys increase distance by requiring additional rope to be pulled to lift an object. Increasing the distance reduces the amount of force needed for the job. By changing the direction of a force, pulleys make it easier to apply the force because it is more convenient to pull down than to pull up. Combining pulleys increases the amount of rope needed to lift an object, so heavy loads can be lifted with even less effort.
Mechanical advantage (MA) is a term that describes how much a machine magnifies effort. The greater the MA, the less the effort needed to lift a given load. There are two types of MA: theoretical and actual. Theoretical MA is the MA most commonly referred to. It is the MA a machine would have if it were perfect. The actual MA, which is always less than theoretical MA, takes into account imperfections in simple machines. The main source of imperfection is friction, the result of two bodies rubbing against each other. Friction always opposes motion, and is present to some degree in almost every machine. Friction is a major problem in pulleys because of the weight on the rope and the movement of the rope on the pulley. Lubricants and bearings are often used in pulleys to reduce friction.
MA is generally determined by dividing the distance the effort travels by the distance the load travels. The higher the MA, the easier it is to do work. A single fixed pulley, such as that at the top of a flagpole, has a theoretical MA of 1, which means for each distance of rope the user pulls in, the flag rises the same distance. Effort is not magnified in this case. The load that can be lifted is equal to the force that is applied by the user. The primary benefit of a single pulley is to change the direction of the force or to move a load to a point (such as the top of a flagpole) that cannot be reached by the user. In reality, the actual MA is slightly less than 1 because of the friction of the rope against the pulley and the friction between the pulley and the axle on which it turns.
Pulleys can offer MAs of greater than 1 if they are movable. A movable pulley is one that is attached to the load to be lifted and therefore moves with the load as the rope is pulled. Even a single pulley, when placed on the object to be moved, provides an MA of 2, meaning that twice the load can be lifted with the same amount of effort. The MA of a movable pulley (or a system of pulleys with a movable part) equals the number of strands of rope coming from the movable part (the load being lifted).

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