# Simple Machines in Engineering

## What are Simple Machines?

Simple machines are the machines with no or very few moving parts. They are used to achieve required work easier by providing mechanical advantage.

For example, a lever is used to reduce the force required to lift heavy objects and pulley is used to change the direction of applied force.

## Mechanical Advantage of a Simple Machine

Due to conservation of energy, Ideal simple machines do not create any energy. They either change the magnitude or direction of the force.

Input Power = Output Power

Input Force x Input Velocity = Output Force x Output Velocity

Mechanical advantage of a simple machine is equal to the ratio of velocity ratio.

Mechanical Advantage = Input Velocity / Output Velocity = Output Force / Input Force

Since the velocity is directly proportional to the traveled distance

Mechanical Advantage = Input Traveled distance / Output Traveled Distance = Output Force / Input Force

## 6 most commonly used Simple Machines

Most complex machines used these days are combinations of the following Six Simple Machines.

1. Wheel and Axle
2. Lever
3. Inclined Plane
4. Pulley
5. Screw
6. Wedge

These above simple machines are used to:

• Change the direction of applied force.
• Transfer the force direction
• Increase or decrease the Force by decreasing or increasing distance.

## Wheel and Axle

Wheel is one of the greatest innovations in human history. A wheel is a circular frame that can rotate about its central axis. At the central axis of the wheel a rod is attached using bearing or free moving. This rod is known as axle. Gear arrangement, car wheels and pulley are the examples of wheel and axle arrangement.

Compared to rectangular surfaces, round surfaces or wheels make a line contact with a surface. Therefore wheels are easier to move because of the reduction in frictional forces. For example, wheels or round rods are used to reduce friction between flat surface and floor to move them easily.

## Lever

Lever is a bar supported at a fulcrum. Weight to be lifted is attached at one end and the force is applied at the other end. As a result, a mechanical advantage greater than one can be achieved. Lever arrangement is used to lift high weight bodies with relatively smaller forces.

Lever Mechanical Advantage = a / b = Output Force / Input Force

## Inclined Plane

Inclined plane is a surface at an angle. It is used to lift heavy bodies by the application of a force less than the weight of the body. Smaller the angle, less force and large displacement is required to lift the body. Therefore force required to raise a body using inclined plane can be given by:

Force = Frictional Force + W sin θ

## Pulley

A pulley consist of a wheel and a rope. At one end of the rope weight is attached and at the other end force is applied to lift the weight. Pulleys are used either to change the direction of applied force or achieve required mechanical advantage. In old days pulley was used to get water from water well.

As shown in the above image, when the pulley is fixed, the force required to lift the weight is equal to the weight. But the direction of the applied force is reversed. Whereas when weight is attached to one moving pulley. Mechanical Advantage becomes equal to two.

## Screw

A Screw consists of a round rod with a helix plane along the length of the screw rod. They are used to convert rotational motion into translational motion. These simple machines are used in bench-vice, screw jack etc.

## Wedge

Wedges are inclined planes that are used to either lift, split or penetrate inside a surface. A wedge shape changes gradually. Nails, chisel, knife, Axe, fork and bow are examples of wedge simple machines.