Machine

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A machine is essentially any device that affects the force or effort that is required to perform a certain amount of work. Machines make difficult tasks simpler by enabling a person to apply less effort in a direction that makes manipulation of the object operated upon much easier. The amount of force required is lessened by increasing the distance over which force is applied. Amount of work done always remains the same. Speed at which an object travels can also be increased, but by extra effort.

The feasibility of a machine is decided by the mechanical advantage which is the ratio of the force exerted on the load to the input force applied. Most machines have efficiencies less than 100%.

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Types of machines

Simple machines can be of four types: the lever, the pulley, the inclined plane and the wheel and axle. All mechanical machines are based on these four simple machines. Complex machines such as engines are combinations of different forms of levers, inclined planes, pulleys, and wheel-axle arrangements.

Following are examples of the different kinds of machines in various forms of the four simple machines.

Lever

A crowbar can be considered to be a form of a lever, since it has a bar that rotates around a fixed point called the fulcrum.

There are three classes of levers:

  • The class 1 lever, in which the fulcrum lies between the effort and the load. An example of this is the seesaw.
  • In a class 2 lever, the fulcrum lies at one end of the lever. The load lies in the middle and the effort is applied at an opposite end. An example of this is the wheel barrow.
  • In a class 3 lever, the fulcrum is at one end, load at the opposite and effort in the middle, as in a fishing rod. The mechanical advantage of a lever is maximised when the load is close to the fulcrum and the effort is at a greater distance from the fulcrum.

Pulley

A pulley consists of a wheel, with a groove over which a rope or chain passes. Pulleys are used to change the direction of force as in a flagpole or window blinds. The mechanical advantage is 1 in such a case. A mechanical advantage greater than 1 is obtained when multiple pulleys are combined. The number of strands of rope on the pulley attached to the load decides the mechanical advantage. However, the friction is increased in such a situation.

Inclined plane

Examples of inclined planes:

  • A ramp - the mechanical advantage of this is the ratio of the *length of the plane to the height to which an object is raised.
  • A screw is a special type of inclined plane, around an axis. The mechanical advantage is related to the pitch and diameter of the screw's axis. Archimedes' screw is an ancient example of a screw being used for the purpose of lifting water from lakes
  • Wedges, which have been used since the ancient times for cutting wood, are examples of double inclined planes.

The wheel and axle

As in the steering wheel of a car, the wheel and axle involves an effort applied at a tangent to the circumference of the wheel. The mechanical advantage is the ratio of the wheel's radius to the axle's radius. The mechanical advantage is larger if the wheel used is greater in diameter.

History of Machines

Machines have been in use for thousands of years. Levers and wheels to perform simple tasks were among the first machines to be used. The Archimedes screw for lifting water is a good example of how machines have been in use. Archimedes, the ancient Greek inventor, is also believed to have used the multiple pulley system to pull ships onto shores.

Water wheels and windmills were used to grind grain and saw wood. The same machines are now used to generate electricity. The Industrial revolution and further periods of scientific growth saw more and more complicated machines being used.