MANUSIA PEMBELAJAR AKAN MENGAJAR DENGAN HATI

MANUSIA PEMBELAJAR AKAN MENGAJAR DENGAN HATI

Senin, 08 Oktober 2012

SIMPLE MACHINES



SIMPLE MACHINES
The machine makes it easier by transferring the quantity of force applied, and the direction of the force or both.
Simple machines are tools which do work with one motion.


There are two kinds of work that run a machine:
The work on the machine is called the incoming work (Win), whereas the work applied by a machine is called the outcoming work (Wout).

In an ideal machine, the incoming work is equal to the outcoming work. For the ideal machine:  

Information :
Force working on the machine is called effort force (Fk).
The force produced by the machine to overcome resistance is called resistance force (Fb).
Part of the simple machine which is working the effort force is called effort arm (dk),
Part of the simple machine which is working the resistance force is called resistance arm (db).

KINDS OF SIMPLE MACHINES :



1.    LEVER
The lever is a simple machine made with a bar free to move about a fixed point called a fulcrum. The lever consists of three parts :
a.     A fulcrum is the fixed point where the rod turns freely,
b.    A load is the thing that the lever lifts or moves and,
c.     An effort is the pushing force to make the objects (load) move.

The position of the fulcrum will determine the amount of the effort that is needed to lift an object.
Fulcrum is placed near the load, less effort is needed to move the object.
       Fulcrum is placed far away from the load, more effort is needed to move the 
       object.



Levers are classified into three classes. The First Class Lever, Second Class Lever and the Third Class Lever. The only difference between them is between the fulcrum, effort and load, which one is located in the middle of the system.

The First Class Lever
In the First Class lever the fulcrum is located in the middle. The load is on one end and the force is on the other.


Second Class Levers
Second Class Lever the fulcrum is on the end, the resistance force, the load, is in the middle, and the effort is at the other end.

 The Third Class Levers
The Third Class Lever, fulcrum is on the end of one side, the effort force is in the middle, and the resistance force, the load is at the other end.



The Mechanical Advantage (MA)
The number indicating the force multiplication done by the machine is called a mechanical advantage.
 

2.    PULLEY
       A pulley is a simple machine consisting of a wheel with a grooved rim in which a pulled rope or chain is run to change the direction and application of a pulling force.
 


Combination of Pulleys
Mechanical advantage in a system of pulley can be measured by counting the sum of rope that pulls a load upwards, to direction of pointer.


3.    INCLINED PLANE

Using an incline plane, the force needed to move the box to the back of the truck is reduced compared to lifting the box straight up.

A knife, a screw, and a wedge are examples of special inclined planes.
 

SCREW  
A screw is an inclined plane which is rotated to a cylinder.
 WEDGE
       A wedge is an inclined plane with one or two inclined sides.




 BIBLIOGRAPHY

Direktorat.2008. SCIENCE for GRADE VIII. Jakarta:direktorat.



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