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Pulleys

Pulleys. A pulley consists of a grooved wheel that turns on an axle with a rope or cable riding in the groove. Its purpose is to either change the direction of a force, or to increase or decrease the magnitude of a force. Parts. Types. There are three types of pulleys : A fixed pulley

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Pulleys

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  1. Pulleys • A pulley consists of a grooved wheel that turns on an axle with a rope or cable riding in the groove. • Its purpose is to either change the direction of a force, or to increase or decrease the magnitude of a force.

  2. Parts

  3. Types • There are three types of pulleys: • A fixed pulley • A movable pulley • Pulley combination

  4. Fixed pulley • A fixed pulley is a simple pulley attached to a beam. It acts as a first-class lever with F on one side of the pulley (axis) and R on the other. It is used only to change direction. • Clinical examples of this can be found in both overhead and wall pulleys and home cervical traction units. In the body, the lateral malleolus of the fibula acts as a pulley for the tendon of the peroneus longus and changes its direction of pull.

  5. Omohyoid and digastric muscles

  6. Obturator internus muscle

  7. A ski lift operates on a fixed pulley system

  8. Moveable Pulley • A moveable pulley - rises and falls with the load being moved. • A movable pulley has one end of the rope attached to a beam then the rope runs through the pulley to the other end where the force is applied. The load (resistance) is suspended from the movable pulley.

  9. Pulley combination • A block and tackle - Consists of two or more pulleys (fixed and moveable).

  10. Mechanical advantage In this simple Fixed pulley system, the force is equal to the load, so the Mechanical Advantage is 1:1 or 1. 10 Kg = 100 N The Mechanical Advantage is calculated like so: Mechanical Advantage = Load / Effort = 100 N / 100 N Mechanical Advantage = 1:1 or 1

  11. In moveable pulley, Each side of the rope carries half the load. Therefore, the force required by the person to keep the load in equilibrium is also half the load. This system has a Mechanical Advantage of 2:1 or 2. 10 Kg = 100 N The Mechanical Advantage is calculated like so: Mechanical Advantage = Load / Effort = 100 N / 50 N Mechanical Advantage = 2:1 or 2

  12. Pulley drives: Toothed Belt and Pulleys Pulleys and Belts

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