# Gravitational Force - PowerPoint

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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        (
• 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
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

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
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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 views: 13 posted: 2/7/2012 language: English pages: 14