# Teach Students About The Single Pulley System

A pulley is a tool used to move objects easily by pulling a rope or cable on the opposite end of a pulley. A single pulley system is essentially a wheel or disk with a grooved rim that sets in a frame and that is free to move around an axis point. There are two different kinds of single pulley systems; there is a single fixed pulley system and a single movable pulley system.

Single Fixed Pulley System

A single fixed pulley is directly attached to a support such as a wooden or metal beam. A single fixed pulley has an axis that is fixed in the center of the disk portion of the pulley and attached to the support. A single pulley system gives you a mechanical advantage over lifting an objects weight. The pulley can be used to elevate an object by pulling downwards as the object you wish to move is raised due to the tension on the rope. A good example of a single fixed pulley system would be raising a bucket of water from a well by pulling one end of the rope as it raises the bucket of water from the well making it easily accessible.

Single Movable Pulley System

A single movable pulley system is attached to the support directly by the rope instead of the pulley like the fixed pulley system would be. Instead of the pulley be fixed to a structure it is on a rope and is fixed to the load you are trying to move. A single movable pulley is capable of lifting and moving the load by pulling upward on the rope. As you pull up on the rope the pulley and the load will then move along the rope towards the end and reach its destination. An example of a movable pulley system would be a zip line. The zip line is fixed to two points with one higher than the other, and the pulley can glide down the wire with a person or object with less friction.

How Fixed and Movable Pulley Systems Work Together

In many cases you can have both a single fixed pulley system and a single movable pulley system in place. You can see how the two work together in a gym. When weights are lifted and released there are many pulleys working together to give the correct amount of resistance and still allowing the person to move the weights. Science fair project for 3rd, 4th, 5th, 6th grade students.

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