Gravitational Force

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Gravitational Force
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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

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Gravity vs. displacement Graph
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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.  

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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  

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Universal Gravitation

• The force on two objects vary inversely with the
  square of the distance between the objects.
• F a 1
• d2
• F G m1 m2 where G 6.67 x 10 -11 Nm2/kg2
• r2

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Mass, distance, force

• How does the mass change the force of gravity?
• How does distance change the force of gravity?

• Mass has a direct change of the force.

• Distance is an inverse square to the force.

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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
• B 1/9 F
• C 9 times F
• D no change in F

3m
Mass A
Mass B
1m
Answer 9 times the Force
Mass A
Mass B
Mass B
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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
• B 1/9 F
• C 9 times F
• D no change in F

3m
Mass A
Mass B
3m
Mass A
Mass B
Answer Tripled Force
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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
• 2/3 F
• 3/2 F
• 6 F

3m
Mass A
Mass B
3 m
Mass B
Answer 3/2 F
Mass A
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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
• ½ F
• ¼ F

3 m
Mass A
Mass A
Mass B
6m
Mass B
Mass A
Answer ¼ F ( Inverse Square )
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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

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Einsteins 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.

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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