It is our common experience that, pull up a bucket of water from a well by using our hand only, is more difficult. But it is much easier if we take help of a pulley to pull up the bucket. Or it is easier to open a nut by the use of a wrench than to open it by hand. Here wrench or pulley is used as machines which are making the job easier.
Def. A machine is a device by which we can either overcome a large resistive force (or load) at some point by applying a small force (or effort) at a convenient point and in a desired direction or by which we can obtain a gain in a speed.
Some definition related to machine
The resistive or opposing force to be overcome by a machine is called Load (L).
The force applied on the machine to overcome the load is called the effort (E).
The ratio of the load to the effort is called the mechanical advantage of the machine. i.e.
The work done on the machine by the effort, is called the work input (Winput)
The work done by the machine on the load, is called the work output (Woutput)
Efficiency of the machine is the ratio of the useful work done by the machine to the work input into the machine by the effort. i.e
But the efficiency is usually express as a percentage
The work output never be greater than the work input because it violate the law of conversion of energy. That means efficiency of the machine never greater than 100%.
If a machine has the efficiency exactly 100% then that machine is known as ideal machine. But in real life, every machine has efficiency less than 100%. That type of machine is known as Actual Machine. If a machine is 80% efficient, it implies that 80% of the total energy supplied to the machine is obtained as useful energy. The remaining 20% of the energy supplied is lost in overcoming friction, etc. which appears as heat energy in its different parts as they get heated up.
In famous Bollywood film 3 idiot, we get two different version of definition of machine
- Defination By Rancho: A machine is anything that reduces human effort. That is, anything that simplifies work, or saves time, is a machine. In example, in summer on the switch and fan is start that is machine, actually today we are surround by the machine.
- Defination By Chatur: Machines are combination of bodies so connected that their relative motions are constrained and by which means, force and motion m be transmitted and modified as a screw and its nut, or a lever arranged to turn about a fulcrum or a pulley about its pivot, etc. especially a construction, more or less complex consisting of a combination of moving parts, or simple mechanical elements, as wheels, lever, cams etc.