The world is rich in complex machines, and we seldom understand their working. We use the word “machine” to describe sophisticated mechanical devices that are powered by an engine or a motor.
Our everyday experience seldom acknowledges devices such as inclined planes, wedges and pulleys as a type of simple machines. Not many of us understand how and why their design may provide an advantage or how they can be best employed.
The primary purpose of simple machines is to reduce the effort needed to perform a task. The term ‘simple machine’ is commonly used by scientists to refer to six different types of devices – Lever, Wedge, Wheel and Axle, Screw, Inclined Plane and Pulley.
Lever
A lever is a stiff beam that rotates around a fixed pivot point (fulcrum) that is located along the beam. Motion at one end of the beam results in the motion at the other end of the beam. One of the simplest examples of a lever is a crowbar which is used to move heavy objects such as rock.
When the operator of the crowbar pushes down on its long shaft, it constitutes an input of force. According to Newton’s third law of motion, for every input force, an output force will be yielded somewhere else. In this case, the dislodging of the stone is considered the output force, resistance force or load. The use of the lever provides the operator with a much greater force than that available to a person who tries to lift the stone with only the strength of his or her body.
Wedge
A knife is one of the common examples of a wedge. Other types of wedges are commonly used as a form of fulcrum for raising objects. Wedges are also placed under objects to stabilize them. For example, using a folded piece of paper under the leg of a table to stop it from wobbling. Similarly, a piece of wood is placed under a door to stop it from closing.
The tools that we make use for cutting chipping such as chisels, scissors, ice picks, axes, electric razors, etc. are all variations of wedges. The part of the key that is used to open a lock is a row of wedges that are used to move pins inside the lock. The tooth in a zipper is a tiny wedge that fits tightly with the adjacent teeth. Wedges in key and zipper are a complex assembly of wedges that work together to reduce the effort needed to perform the task.
Wheel and Axle
The steering wheel and screwdrivers are typical examples of wheel and axle. A small force applied at the edge of the wheel is converted to a more powerful force at the axle by rotation. This effect can be reversed by applying a large force to the smaller axle resulting in a smaller force at the larger wheel with greater rotational speed.
Screw
A screw acts as an inclined plane that has been wound around a shaft. They are commonly used as a fasting mechanism. The rotation of the threaded shaft is converted into movement in either direction along the axis of rotation.
Inclined Plane
An inclined plane is used to raise or lower heavy objects. The friction on the ramp is small. Hence a reduced force is required to raise a heavy object vertically. But the objects must be moved through a great distance along the ramp to achieve this advantage.
Pulley
A single fixed pulley and a cord attached to it allows for a change in the direction of the force applied to an object. Pulleys can be used in complex combinations to provide larger mechanical advantages such as with the design of ‘block and tackle.’
It must be noted that simple machines only magnify or reduce the forces applied to them; they do not change the total amount of work needed to perform the overall task.