Wednesday, November 3, 2010

Science Form 2 Rujukan/Notes

SCIENCE - FORM 2
Simple Machines
                                                                                         
                         
                     
                        
LEVERS

Simple machines

1.   A machine is an instrument used to overcome a larger load with less effort or force.

2.   Simple machines include :
      (a)   lever           (d)   wheel and axle
      (b)   wedge        (e)   screw
      (c)   pulley         (f)    inclined plane  

3.   Several simple machines are combined together to form a complex machine. The examples of
      complex machines are cars, aeroplanes, food processes and tractors.

4.   A lever consist of :
      (a)   A piece of bar which is free to turn about a fixed point or fulcrum.
      (b)   An effort is the force applied to overcome another force or the load.

5.   A simple lever is shown in the Figure above.
      
      (a)   The perpendicular distance of the load from the fulcrum is called load distance.
      (b)   The perpendicular distance of the effort from the fulcrum is called effort distance.

6.   Levers are called force magnifiers because they magnify the amount of a force.

      
Types of Levers

First class lever

       
1.   The first class lever is indicated by the fulcrum placed between the effort and the load.

2.   The effort and load act in opposite directions from the fulcrum.

3.   When the distance of effort from the fulcrum, a small force is used to move a large load.
      

4.   When the distance of load from the fulcrum is greater than the distance of effort from the fulcrum,
      a large force is used to move a small load.
      
       
Second class lever

1.   In the second class lever, the load is between the fulcrum and the efford.

2.   The load acts in opposite direction with the effort.

3.   The turning  effect of the effort increases when the distance of effort from the fulcrum is greater
      than the distance of load from the fulcrum.

4.   A large force is produced to overcome a large load.

      
Third class lever
             
      

1.   In the third class lever, the effort is between the fulcrum and the load.

2.   The load moves a longer distance, but the effort moves a shorter distance.

3.   A large force is applied to move a small load.

4.   A small movement produces a large movement.

         
The moment of a Force

1.   When someone uses a bottle opener to open a bottle cap, some force is applied on the bottle
      opener.

2.   The moment of a force is the turning effect used when some force is applied to open the bottle cap.

       
3.   It is easier to open the bottle cap by holding the can opener at the end of the handle as shown in
      the Diagram above (b) because the turning effect is greater.

4.   The turning effect depends on :
      (a)   The amount of force used
      (b)   The perpendicular distance

        
      
6.   The direction of the turning effect determines wheter the moment of a force is a clockwise or
      anti-clockwise moment.

      
Applications of the lever principle

1.   Figure above shows a balanced see-saw. John who is 50 kg sits 3 m away from the fulcrum. Adam
      who is 30 kg sits 5 m away from the fulcrum.

        
      If John moves 1.5m away from the fulcrum, how far from the fulcrum should Adam sits to keep the
      see-saw in balance?
      Solution
      John's weight x John distance from the fulcrum = Adam's weight x Adam's distance from the
      fulcrum (y)
   
2.   Calculate the amount of effort required to keep the following lever in balance.

           


      Solution :
      
Load x load distance
      = Efford (E) x effort distance.

      

APPRECIATING  THE INNOVATIVE EFFORTS IN THE DESIGN OF MACHINES TO SIMPLIFY WORK


1.   An invention is the makingh of new machines, engines, tools or other useful objects that no one
      else has thought of before or it can be an improvement on something that has been produced by
      someone else.

2.   Since ancient days, people have invented many types of machines and tools to make their work
      easier.

3.   In ancient Egypt, shaduf was used to transfer water from one place to another and to irrigate farm
      lands.

         
4.   We should be grateful and appreciate the inventions  done by scientists to make our work easier
      and our lives more comfortable.

5.   Modern life demands sophisticated and afficient machines to carry out complex tasks.

6.   Modern tractors were invented to replace animals to plough farms and to harvest crops.

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