Pulley

Pulley is a simple metallic or wooden machine which uses a wheel and a rope for lifting heavy loads. Nowadays, for carrying small loads, plastic pulleys are also being used and available in the market. We can rotate it very freely just by the axis passing through its center. It helps in changing the direction of the force which helps in making it easier for the people to lift any object. With the help of a pulley, one can pull down one end of the rope to lift ten Kgs objects which are one meter high.

Types of Pulley

Mainly, there are two types of and those are fixed pulley and movable pulley. These type of pulleys are explained below –

Fixed Pulley – The pulley in which it’s block is fixed on a high platform is known as fixed pulley. An extensible string is passed over the groove where one end of it is attached to the body for being lifted and the other end is free to use. Usually, these types of pulleys can be seen in walls, floors and ceilings. In a fixed pulley, its system is fixed but the rope can move freely.

Movable Pulley – The pulley in which it’s block is not fixed but it carries a load is known as movable pulley. In a movable pulley, an extensible string is tied around the groove where one end of it is fixed to fixed support while the other end of it is always kept free so that the efforts can be applied. As the effort is applied on it, the block which is with the loads moves upward altogether. In the mechanism of a movable pulley, wheels carry the load instead of ropes. In this type of pulley, a little amount of manual work is required.

Compound Pulleys – Compound pulley meaning combines the functions of both fixed and moving pulleys. In this case, the movable pulley links with the rope attached to a fixed one. Accordingly, one can mount the weight on the movable wheel to shift its position. It helps one to redirect force as per one’s requirements, while also altering the overall workload of that force. 

Therefore, this sums up the three distinct types of pulleys. 

Formula for Pulleys

Mechanical advantage can be calculated by dividing load by effort

Load can be calculated by multiplying mechanical advantage with effort.

Effort can be calculated by dividing load by mechanical advantage.

For finding out the velocity ratio, we have to divide distance of effort by distance of load. 

(The ratio of the distance moved by effort and load is the velocity ratio).

Mechanical Advantage of Pulley

Mechanical advantage has been used to measure the effectiveness of the pulleys. It can be calculated when the friction is absent. All the machines have some friction but sometimes somehow if all of the machines overcome friction, the mechanical advantage is somewhat always greater than in the real world.

The mechanical advantage of any pulley is the ratio of the force which is utilized in the work to the force which is applied in the work. During its calculation, we used to make assumptions about the weights of pulley and ropes that they are negligible and there is no loss of energy which occurs due to the friction which is the wheel and ropes. There is one more assumption that the ropes which are used during the operation, do not elongate during the process.

The effort which is required for lifting the weight is equal to the weight of the body in itself in the single loop system.

The effort of pulling the weight becomes half when there are two loops present in the pulley.