Counting the lengths of rope between the pulleys that sustain the load is a simple approach to establish **the optimal mechanical advantage** of **a pulley system**. Only one section of rope is shown in Figure 1(a) to sustain the load. As a result, the mechanical advantage is 1.0.

The mechanical advantage can also be determined by balancing forces at a point close to where the rope passes through the pulleys. The two equal and opposite forces are the weight of the rope itself (mg) and the tension in it (T). Since T is known, we only need to consider mg. There are two ways to do this: either by considering how much mass there is near the center of gravity or by assuming that the mass is uniformly distributed throughout the rope.

If we assume that the mass is uniformly distributed then the total mass of the rope is simply its diameter times its length (or volume if you will). If we call this quantity m then the center of gravity will be half way down the rope and it will have **mass m/2**. Now we can say that the force of gravity acting on this center of gravity must be T/2 because it is equally balanced by the tension in the rope. This tells us that the mechanical advantage is equal to T/g which can also be written as g/T since they are equal numbers.

To calculate a pulley's mechanical advantage, just count the number of rope sections that support **whatever object** you are raising (not counting the rope that is attached to the effort). In a one-pulley system, for example, the MA is 1. The MA in a two-pulley system is 2. In **a three-pulley system**, it is 3, and so on.

As you can see, the mechanical advantage of a pulley system increases as more pulleys are added.

Since the force required to lift the object is equal to its weight, we can divide 35 by 3 to find that the object needs to be lifted about 11.1 feet high in order for it to be considered balanced by gravity alone. This means that the mechanical advantage of our three-pulley system is approximately 10. Once you know the mechanical advantage of your system, then multiplying the load by this value will give you **the maximum load** that can be pulled through the system.

The major advantage of using pulleys is that the effort required is less than that required for standard weight lifting. To put it another way, it minimizes the amount of physical force necessary to raise large items. It also alters the direction of the applied force. Instead of pulling on the weight directly, you are actually pushing against it with the help of the rope. This allows you to lift weights that you could not otherwise move.

A pulley system can be used in place of standard weights because the force required to drive the rope through the pulley is much less than the force required to lift the same weight directly. For example, if you were to try and lift **100 pounds** straight up, you would need sufficient strength to pull **this weight** up above **your head**. However, if you used a pulley system, then you would only need enough force to push against the weight with the rope. In this case, it requires only 50 pounds of force to lift 50 pounds via a pulley system.

There are two types of pulleys: fixed and movable. With a fixed pulley, the size of the hole in the center cannot be changed; therefore, any object that fits through the hole will use that pulley. With a movable pulley, the size of the hole can be altered by moving one of the sides of the hole closer or farther away from the other side.

A basic machine's mechanical advantage, such as a pulley, is the factor by which the machine alters the force supplied to it. A machine's ideal mechanical advantage is its mechanical advantage in the absence of friction. In other words, the force exerted to this sort of pulley does not grow. Instead, the force increases only the distance that the cord travels.