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					Gravitational Force
       4 Forces of the Universe
• Nuclear : Strong forces holding the
  nucleus of an atom together (gluon)
• Weak : Forces as a result of some
  atoms that decay the nucleus        (
  radioactive )
• Electromagnetic : a force based on
  electricity, magnetism and light
  properties
• Gravitational : The weakest force
  caused by the 2 factors, MASS and
  DISTANCE
Gravity vs. displacement Graph
Henry Cavendish 1731 - 1810
•Education. At age 18, (1749) he
entered Cambridge in St. Peter's
College. He left without graduating
four years later. His first paper
Factitious Airs appeared 13 years later.

•Eccentric in life. Henry Cavendish
had a peculiarly odd demeanor. He was
morbidly shy of women and strangers
and avoided ever speaking to
them. Henry Cavendish was extremely
wealthy, he became the single largest
holder of bank stock in England.
    Cavendish Experiments
• Cavendish's most famous
  accomplishment in science took place
  during the years 1796 - 8 during which he
  established the mean density of the
  earth to be 5.448. The current estimate is
  5.5. Verification of G, Gravitational
  Constant
• Hydrogen (Inflammable air). Cavendish
  is generally credited with the discovery of
  inflammable air
           Universal Gravitation
• The force on two objects vary inversely with the
  square of the distance between the objects.
• Fa 1
      d2
• F = G m1 m2 where G = 6.67 x 10 -11 Nm2/kg2
         r2
 Mass, distance, force
• How does the mass change the force of gravity?
• How does distance change the force of gravity?
   Mass 1      Mass 2      Distance     Force Of Gravity
     1            1            1                 F
     2            1            1                 2F
     1            2            1                 2F
     2            2            1                 4F
     1            1           1/2                4F
     1            1            2                 1/4

 • Mass has a direct change of the force.
 • Distance is an inverse square to the force.
  Gravitational Problem #1
• Gravitational force of attraction F exists between two point
  masses. Mass A distance is 3m and B is changed to only
  1m, the gravitational attraction between the masses has
  changed by:
• A Tripled F
                                                 3m
• B 1/9 F
• C 9 times F
• D no change in F                Mass A                  Mass B

                                                     1m



                                            Mass A     Mass B
  Answer: 9 times the                             Mass B

  Force
  Gravitational Problem #2

• Gravitational force of attraction F exists between two point
  masses, mass A and B are separated by a fixed distance.
  After mass A is tripled and B remains the same, the
  gravitational attraction between the masses is:
• A Tripled F
                                                 3m
• B 1/9 F
• C 9 times F
• D no change in F                Mass A                  Mass B

                                            3m


                                Mass A                  Mass B

 Answer: Tripled Force
             Gravitational Problem #3
 • Gravitational force of attraction F exists between two point
   masses, mass A and B are separated by a fixed distance.
   After mass A is tripled and B is halved, the gravitational
   attraction between the masses is:
 •   1/6 F
                                       3m
 •   2/3 F
 •   3/2 F               Mass A                   Mass B
                                          3m
 •   6F

                                                   Mass B
Answer 3/2 F             Mass A
    Gravitational Problem #4
• Gravitational force of attraction F exists between two point
  masses. After the distance is doubled between A and B, the
  gravitational attraction between the masses is:
• 2x F
• 4x F                                  3m
• ½F
• ¼F
                          Mass A                  Mass B

                             6m


                                                  Mass B
   Mass A

     Answer : ¼ F ( Inverse Square )
    Gravitational Problem #5
• Find the Force of attraction (gravity) between two
  7.26 kg Bowling balls separated by .3 m.
• F = G m1 m2
           r2
• F = (6.67 x 10 -11 Nm2/kg2) ( 7.26kg) ( 7.26kg)
           (0.30m)2

•   F = 6.67 x 52.7076 x 10 -11 N m2
•       .09 m2
•   F = 351.559692 / .09 x 10 -11N
•   F = 3906.2188 x 10 -11N
•   F = 3.91 x 10 -8 N
             Einstein’s Gravity??
• “The editors of Scientific American have asked
  me to write about my recent work which has just
  been published. It is a mathematical investigation
  concerning the foundations of field physics”
• He discussed his special and general theories of
  relativity and his work toward a unified field
  theory in a 1950 Scientific American article. At
  the time, he was not convinced that he had
  discovered a valid solution capable of extending
  his general theory of relativity to other forces. He
  died in 1955, leaving the problem of Gravity
  unsolved.
                  Summary
• Gravity is the weakest force
• Gravity is only a force of attraction
• Gravity is dependant on distance and mass
• The force of gravity changes directly with the
  mass
• The force changes inversely to the square of
  the distance

				
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posted:2/7/2012
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