Physics Lesson 7 - Simple Machines

 SIMPLE MACHINES

MACHINE is a mechanical device which make work easier, however it does not create energy but must be supplied with energy in order to do work 

   Types of Machines

      1.  Machine use to transform energy

            a) generator – transform mechanical energy to electrical energy

            b) motor -  transform electrical energy to mechanical energy.

            c) steam turbine ( gas turbine), heat engine – transform heat energy to mechanical energy.

     2.  Machine use to transfer energy from one place to another.

          Ex.  Connecting rod, crankshaft, drive shaft, and rear axle transfer energy from the combustion chamber in the  cylinders of the car engine to the rear wheels.        

 

     3.  Machines use to multiply force

                     Ex   Pulley system

     4.  Machine use to multiply speed.

                     Ex.  Bicycle wheel moves faster than the sprocket

     5.  Machine use to change direction of force.

                     Ex.  Pulley in construction carry load upward by applying a force downward.

    

    Kinds of Machines

            1.  Lever                      3.  Wheel and axle                  5.  Screw

            2.  Pulley                     4.  Incline plane                       6.  Wedge

    Actual Mechanical Advantage ( AMA ) is the ratio of the output force ( F_o ) exerted by the machine on the load to the input force ( F_i  ) exerted by the operator.

                                    AMA =  F_o/ F_i   

    If  AMA  > 1  ==>  increase of force. Examples: vise, crow bar,  block and tackle

    If  AMA <  1  ==>  increase in speed. Example : bicycle chain and sprocket.

Ideal Mechanical Advantage ( IMA ) is the ratio of the distance ( Si ) through which the input work acts, to the distance ( So ), through which the output work acts.

                        IMA =  Si / So 

Considering friction :           

                      Wo  <  Wi

                        Fo So <  Fi Si  ,   divide both numerator and denominator by  Fi So

                        Fo/ Fi  <  Si / So

                         AMA  <  IMA 

Efficiency ( Eff ) is the ratio of the output work to the input work express in percentage.

                        Eff =  Wo / Wi  =  FoSo / FiSi  , divide both numerator and denominator by Fi So

                        Eff = Fo / Fi ¸  Si / So  =  AMA / IMA    

  IMA  of the individual Machines :

  1.  Incline plane :  IMA = Si / So =  L / h  =  csc a ,  a  is the angle of inclination

  2.  Wheel and axle :  IMA =  R / r  =  D / d  ,  R = radius of the wheel ,  r = radius of the axle

                                                                      D = diameter of the wheel ,  d = diameter of the axle

  3.  Screw :  IMA =  2pi L / p  ,  where  p =>  thread pitch

  4.  Pulley :  IMA = Si / So

  5.  Lever :   IMA =  Si / So   

Think, Believe, Dream and Dare

An eight-year-old boy approached an old man in front of a wishing well, looked up into his eyes, and asked: "I understand you're a very wise man. I'd like to know the secret of life."

The old man looked down at the youngster and replied: "I've thought a lot in my lifetime, and the secret can be summed up in four words.

The first is think. Think about the values you wish to live your life by.

The second is believe. Believe in yourself based on the thinking you've done about the values you're going to live your life by.

The third is dream. Dream about the things that can be, based on your belief in yourself and the values you're going to live by.

The last is dare. Dare to make your dreams become reality, based on your belief in yourself and your values."

And with that, Walter E. Disney said to the little boy, "Think, Believe, Dream, and Dare."

~ Author Unknown ~



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