Simple Machines

Simple Machine
Is a device by which the magnitude, direction or method of application of a force is changed for the sake of gaining some practical advantage.

Principle of Work
An ideal or frictionless machine, the work done by the machine (output) is equal to the work done upon the machine or the energy applied to it (input). Otherwise the useful wprk output diminished is due to the work done by the friction.

Work Input = useful work + friction work

Efficiency
Is the ration of the output to the input.

Efficiency = work output / work input = power output / power input

Actual Mechanical Advantage
The AMA (Actual Mechanical Advantage) of a machine is

AMA = force ration = force exerted by machine on load / force used to operate machine

Ideal Mechanical Advantage The IMA (ideal mechanical Advantage)

IMA = distance ratio = distance moved by input force/ distance moved by load

Since friction is always present IMA is always greater than the AMA.

Kinds of Simple Machine

a. lever – is a rigid bar, straight and or curved, which rotated about a fixed point called the fulcrum.

b. Wheel an axle- is consist of a large and a small wheel rigidity joined to the same axle. The rope to which the is applied is wound around the large wheel while the rope that carries the weight is around the smaller but in opposite sense, so that the unwinding of the results in the winding of the second.


c. Pulley – is a wheel with a grooved rim through which a rope or cord passes. The effort (pulling) and the resistance (weight) are applied to either end of the rope.

d. Inclined plane – when a body rests on an inclined plane, the weight of the body acts vertically while the reaction of the plane is perpendicular to its surface, the angle between two forces being t the angle between the plane and the horizontal.

e. Screw – is a metal cylinder, grooved in and advancing spiral to its outer surface. From the point of view of Physics, this is a combination of the inclined plane and the lever. If p is the pitch of the screw, that is the distance from one thread to the next, to the work done in complete revolution will be\
R x p


Referrence:
page 69 Physics Committee book
Far Eastern University
2004