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Simple Machines

  • A simple machine is a device by means of which a force is applied at one point and is used to overcome a load at some other point.
  • Simple machines are simple tools that can be used in the home, offices, schools, and other places.
  • However, there are some machines that are not confined to workshops and industries and are found in our homes, e.g. screw, spoons, hoes, can openers, brooms, etc.
  • With the aid of these machines, we are able to do work quickly and easily.
  • Therefore, a machine is a device that makes work done conveniently.
  • Levers are common examples of simple machines, e.g. knives, forks, spoons, axes, hoes, scissors, tin cutters, brooms, pliers, hammers, etc.
  • Levers are classified into three classes, based on the relative position of the effort, load, and fulcrum. The classifications are:
    • First Class Levers: The fulcrum or pivot is between the effort and load. E.g. Pliers, scissors, etc.
    • Second Class Levers: The load is between the fulcrum, and effort. E.g. Wheel barrow, nut cracker, etc.
    • Third Class Levers: the effort is between the load and the fulcrum. E.g. Sugar tongs, etc.

Examples of Simple Machines (Photo Credit: JustScience.in)

Types of Simple Machines
  • Wheel and Axle
    • The wheel and axle is a form of simple machines made of two wheels of different diameters that are over rigidly fixed on the same axle.
    • For wheel and axles, applying effort to the string or rope causes the load to be raised by the string wound around the axle.
    • Wheel and axles can be used for lifting heavy loads from any place below the wheel and axle’s position.
    • The wheel and axles is used for drawing water from a well, etc.
  • Screw
    • A screw consists of the handle called effort, arm, pitch, and thread.
    • A screw is an inclined plane wrapped around a cylinder to form a thread.
    • Examples of screws include carpenter screw, bolts and nuts, and car jack, etc.
Parts of a Screw
    • A simple screw consists of a rod which has a thread.
    • The distance between two threads is called pitch of the screw.
    • It is the point of rotation or the point at which effort is applied.

Anatomy of a Screw (Photo Credit: WonKeeDonKeeTools.co.uk)

How a Screw Works
    • For screw to operate, when the effort moves a complete circumference of a circle, the load moves a corresponding distance which is the pitch.
    • The longer the effort arm, the easier the operation done by the effort.
The Work of a Screw
    • Screws are used daily for making holes in hard objects.
    • Screws make it easier to hold different parts of an object together.
  • Gears
    • A gear is a machine which allows work to be done easily and helps to transfer energy from one engine to the driving wheel.
    • The principle of a gear is similar to that of a screw.
    • Gears are toothed.
    • They are made up of two wheels. One wheel, called the driving wheel, drives the other wheel, called the driven wheel.
    • The teeth of the two wheels are made to interlock such that in the application of effort on the driving wheel, the driven wheel rotates simultaneously and the vehicle moves.

Examples of Gears (Photo Credit: Pexels.com)

Uses of Gears
    • Transmission of energy from one point to another in a mechanical device.
    • Transmission of power.
    • Transmission of motion.
    • Converting between the types of motion. E.g. From linear motion to rotary motion, etc.
Efficiency and Care of Simple Machines
  • The efficiency of a machine is defined as the ratio of work output and input expressed in percentage.
  • Efficiency, ε = (work output/work input) × 100%
  • The advantage of using machines is to make work easier, but not all energy put into a machine is used to do work.
  • Some of that energy is lost as heat or wasted to overcome friction.
Level of Efficiency of a Machine
  • The efficiency of a simple machine in a simple pulley system can be defined as:
    ε = (load × distance moved by the load)/(effort × distance moved by the the effort)
  • Mechanical advantage (M.A.) of a machine is the ratio of the load to the effort.
    M.A. = load/effort
  • Velocity ratio (V.R.) of a machine is the ratio of the distance moved by the effort to the distance moved by the load.
  • Therefore, Efficiency, ε = (M.A./V.R.) × 100
Care of Machines
  • Machines require regular maintenance to ensure their efficiency.
  • Different machines have different experts or specialists and it is advisable to use the appropriate specialist when needed.
  • Machines can be maintained by:
    • Using oil or ball bearings to reduce friction on the moving parts.
    • Regular removal of dirt from the machine.
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