Pulleys

Introduction

A pulley is a simple machine used to change the magnitude and/or direction of an effort (applied) force required to lift a load. It consists of a rope that passes over a grooved wheel. There are three basic types of pulleys: fixed, movable, and compound. A fixed pulley is attached to a solid support with one end of the rope attached to the load. A force equal to the load is applied in one direction to make the load move in the opposite direction.

A movable pulley is attached to the load, and one end of the rope is attached to a solid support. A force equal to only half the load is required to lift it, but the rope must be pulled twice as far as the load is raised. A compound pulley uses more than one pulley. The rope is attached to the innermost pulley and wound around subsequent pulleys in a spiral configuration. The more pulleys used, the less force required to lift the load. Mechanical advantage (MA) is a value that tells the number of times a pulley increases your applied force. In this activity, you will use a Force Sensor to measure the effort force for three different pulley systems, and then determine the mechanical advantage of each system.

Objectives

In this experiment, you will.

• Use a Force Sensor and NXT to measure the effort force when using a pulley.
• Calculate actual mechanical advantage and ideal mechanical advantage.
• Determine efficiency.
• Make conclusions about pulley systems.