PULLEY A pulley is a wheel with a groove along its edge forholding a rope or cable. It is a simple machine that helps changethe direction and point of application of a pulling force. Pulleysare usually used in sets designed to reduce the amount of forceneeded to lift a load. The magnitude of the force is reduced, but itmust act through a longer distance. Consequently, the amount ofwork necessary for the load to reach a particular height is thesame as the amount of work needed without the pulleys. Pulleys can be found in many different applicationsaround us. Not only are they used for the obvious lifting of objects,such as by cranes, but they are also used in modern automobilesand airplanes. Pulleys are also essential for most machines insome form or other.
EXAMPLES OF PULLEYS Block and Tackle Pulley Movable Pulley Fixed Pulley
WEDGE A piece of material, such as metal or wood, thick at one edge and tapered to a thin edge at the other for insertion in a narrow crevice, used for splitting, tightening, securing, or levering.
LEVER A lever is a simple machine that makes work easier for use; it involves moving a load around a pivot using a force. Many of our basic tools use levers, including scissors (2 class 1 levers), pliers (2 class 1 levers), hammer claws (a single class 2 lever), nut crackers (2 class 2 levers), and tongs (2 class 3 levers).