Pulley

Definition

A pulley is a simple machine consisting of a grooved wheel over which a rope or cable runs. Pulleys are commonly used to change the direction of a force or to multiply the magnitude of a force, making it easier to lift or move heavy objects.

5 Must Know Facts For Your Next Test

1. Pulleys can be used to change the direction of a force, allowing a person to pull in a different direction than the direction of the load.
2. The mechanical advantage of a pulley system is the ratio of the load force to the applied force, which determines how much the system can multiply the input force.
3. The tension in the rope or cable running through the pulley must be equal to the load force divided by the number of rope sections supporting the load.
4. The ideal mechanical advantage of a pulley system is the number of rope sections supporting the load, which is the theoretical maximum mechanical advantage that can be achieved.
5. Pulley systems are often used in cranes, elevators, and other mechanical devices to lift or move heavy objects with less effort.

Review Questions

• Explain how a pulley can be used to change the direction of a force.
  • A pulley can be used to change the direction of a force by changing the direction of the rope or cable that is used to apply the force. For example, if a person is pulling on a rope that is running over a pulley, the direction of the force they are applying will be different from the direction of the load that is being lifted. This allows the person to pull in a more convenient direction, making it easier to lift the load.
• Describe how the mechanical advantage of a pulley system is calculated and how it affects the amount of force required to lift a load.
  • The mechanical advantage of a pulley system is calculated as the ratio of the load force to the applied force. This ratio determines how much the system can multiply the input force. The more rope sections supporting the load, the higher the mechanical advantage and the less force is required to lift the load. The ideal mechanical advantage is equal to the number of rope sections supporting the load, which is the theoretical maximum mechanical advantage that can be achieved.
• Analyze the relationship between the tension in the rope or cable running through a pulley and the load force being lifted, and explain how this relationship affects the design and use of pulley systems.
  • The tension in the rope or cable running through a pulley must be equal to the load force divided by the number of rope sections supporting the load. This relationship is crucial in the design and use of pulley systems, as it determines the strength and size of the rope or cable required to safely lift a given load. If the tension in the rope or cable is too high, it can lead to failure and potential injury or damage. Conversely, if the tension is too low, the pulley system may not be able to effectively lift the load. Understanding and properly calculating the tension in the rope or cable is essential for the safe and efficient use of pulley systems.

Related terms

Mechanical Advantage:

The mechanical advantage of a pulley system is the ratio of the load force to the applied force, which determines how much the system can multiply the input force.

Tension:

Tension is the force exerted by the rope or cable running through the pulley, which must be equal to the load force divided by the number of rope sections supporting the load.

Ideal Mechanical Advantage: The ideal mechanical advantage of a pulley system is the number of rope sections supporting the load, which is the theoretical maximum mechanical advantage that can be achieved.