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 exerted by the machine on the load to the input force 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 q  ,  q 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 =  2p L / p  ,  where  p =>  thread pitch

  4.  Pulley :  IMA = Si / So

  5.  Lever :   IMA =  Si / So