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Pulleys and pulleys


Have you observed in person, in sports programs or in movies, that in fitness centers, weight machines are full of hard disks around which there is a cord, on which loads are attached? What are worth for?

These discs are called pulleys or pulleys. They are discs with a channel through which a wire or rope passes, in which a load is attached.

Fixed pulleys

The fixed pulley facilitates an effort to change the direction of the force that would be required. In this case, as noted in the figure, the force required to balance the body is equal to the force held by the person. However, to lift the load, we have to pull down, which makes the job easier.

Moving pulleys

Movable pulleys decrease the intensity of the effort required to support a body, as part of that effort is made by the ceiling, which supports the joint.

Notice in the picture below how the movable pulley can make the job easier.

  • With a movable pulley, the force required to balance the load is divided by two (21).
  • With two movable pulleys, the required force is divided by four (22).
  • With three, it is divided by eight (23), and so on.

We now know why there are so many pulleys in a weight room. They have made the effort we want to make viable, usually by changing the direction of the force needed to lift the weights to work the desired muscles.