A pulley facilitates work by diverting and increasing force. It aids in the reversal of an individual's lifting power. When a user pulls on a rope, the pulley raises the weight. A pulley lowers the effort required to raise a weight by half when two ropes and wheels are employed. This is because one can pull on both ropes at the same time, thus reducing the effort required. Pulleys have several uses in industry. They are commonly used by fishermen to lift heavy loads over obstacles such as rocks or bushes. On fishing boats, they are also used to lift nets or catch fish without hurting them. In construction, they are often used to lift heavy objects such as pipes or cables from the ground up into a building site. Pulleys are also used in mining to help lift heavy materials such as gold ore back out of a mine pit. Pulleys can be divided into three main types: single-block, double-block, and tri-block. In a single-block pulley, there is only one block that lifts weights off the ground. This type of pulley is easy to make using a block and a cord or rope. Double-block pulleys have two blocks that cooperate with each other to lift weights. Tri-block pulleys have three blocks that work together to lift weights. All types of pulleys use wheels or cones to turn freely along with the blocks.