pulley

                                      Pulley

A pulley is a grooved wheel which is rotated about a fixed axis by a rope which passes round it. The axis is supported by a frame work or block and the whole structure may be used either as a fixed pulley or a movable pulley.

The Fixed Pulley:

       This is used to alter the direction of a force and enables traction or resistance to be applied at any angle. the pulley block is fixed to some suitable support and the rope which passes round the wheel is attached to the weight at one end and the effect is effort is applied at the other. The fixed pulley system is used in the body by some muscles to allow them to be inserted at a more advantageous angle. 

Eg: Digastric and omohyoid muscles pull round fibrous loops 

The Movable Pulley:

         This device is used to gain a mechanical advantage when lifting heavy weights. One simple combination is in common use for lifting the trunk for suspension exercises.

Upper pulley is fixed to an overhead support ,to which one end of the rope is attached .the rope is wounded round the movable pulley ,the effort being applied at the free end. The tension is the same in all parts of the rope.

Mechanical advantage=W/E

Where,

           W- weight

           E- effort