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Machines

What are simple machines and terminologies

A machine is a device through which we can either overcome a large resistive force present at some point by applying a small force at a specific point in a desired direction or obtain a gain in speed.

These machines have been used for centuries not only to make work easy, but also to make it efficient and safe. As the name suggests, the construction of simple machines are not complicated and they are used for day-to-day simple works. The other characteristic feature of simple machines is that they do not convert energy from one form to another. Complicated machines such as bicycles and screwing machines are made up by combining two or more simple machines.

Simple machines can be broadly classified into two categories.

  • Lever
  • Inclined plane

These two types are further divided into sub-categories, as shown in the given diagram.

A lever is a rod which moves freely about a fixed point called the fulcrum. 

Parts of a Lever

Levers are of three types depending on the position of the fulcrum, load and effort. 

Lever of first order: Fulcrum is situated between the load and the effort. E.g., see-saw, crowbar, beam balance

Lever of second order: Load is situated between the fulcrum and the effort. E.g., mango-cutter, wheel barrow, nut cracker

Lever of third order: Effort is situated between load and the fulcrum. E.g, pair of tongs, fishing rod

An inclined plane provides a sloping surface over which heavy things can easily be lifted or rolled down.

There are certain common terms that are used for almost every simple machine. Let us understand these terminologies first.

Machine Terminology

  • Effort — The force applied to a machine to do mechanical work is called effort.
  • Load — The force applied on an object by the machine is called load. When a crow bar is used for lifting an object, the weight of the object is the load, as that is the amount of force the simple machine has to apply to lift the object.
  • Fulcrum — When a machine does mechanical work by turning on a point, the point of rotation is called the fulcrum. In the given picture, the middle point is the fulcrum of the seesaw.

  • Input Energy — The work done on a machine or the energy supplied to a machine is called input energy.
  • Output Energy — It is the work done by the machine or the energy obtained from the machine.
  • Principle of Ideal Machine — In an ideal machine, the output energy is equal to the input energy. Therefore, mathematically we can express it as. This is called the principle of machine.
  • Mechanical Advantage— It is the ratio of the force obtained from the machine to that applied to the machine. In simple words, we can say
  • Velocity Ratio— It is defined as the ratio of the displacement of effort to the displacement of load.
  • Velocity of load (VL) =dLtVelocity of effort (VE) =dEtVelocity ratio=VEVL=dEtdLt=dEdL
  • Efficiency — The ratio of the energy obtained from the machine to that supplied to it is known as the efficiency of the machine. It is obtained by dividing the amount of work done by the machine by the work done on the machine.
  • In an ideal machine, all the input energy is converted into output energy i.e., the efficiency of an ideal machine is 100%. In real life, no machine can have 100% efficiency because some amount of input energy always gets lost to overcome the friction between the different parts of the machine.

  • Relation Between Mechanical Advantage (M.A.) and Velocity Ratio (V.R.): Assume a machine is doing a work in time t to overcome a load L by the application of effort E. Let the displacement of effort be dE and of load be dL.Work input=Effort×Displacement of effort=E×dEWork output=Load×Displacement of load=L×dLη=work outputwork input=L×dLE×dE=LE×1dEdLLE=M.A. and dEdL=V.R.η=M.A.V.R.M.A.=η×V.R.
where, η is the efficiency the machine.
 
We must take care of machines to minimiz…

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