Gravity Equation

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Gravity Equation
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• F force of gravity
• G gravitational constant (610-11)
  0.00000000006
• M1 mass of body 1
• M2 mass of body 2
• S2 distance between
• M1 M2 squared

M1 M2
G
F
S2
2
Gravity
M1 M2
G
F
S2

• 1. The force of gravity is not effected by other
  bodies present.
• 2. The force of gravity is equal but oppositely
  directed.
• Fma Newtons second law

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Gravity
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M1M2
F
G
F
S2
M1
M2
M1A1

M2A2
If the force is equal and opposite, then
F MA for both
M1A1 M2A2
M2 is larger than M1
so, A1 must be larger than A2 if they are equal.
Across a crowded room, you and an airplane
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Gravitational Constant

• G 610-11 - a very small number
• 0.00000000006
• What is the attraction between you and the person
  next to you?
• What is the attraction between you and the earth?

M1 M2
G
F
S2
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Gravity
M1M2
If masses stay the same, but the distance
increases, how does the force of gravity
change?
G
F
S2
M same

F lt
S increases
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Gravity
M1M2
If distance stays the same, but the masses
increase, how does the force of gravity
change?
G
F
S2
increase

F gt
same
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Gravity

• Will a body always have the same mass if the
  volume remains constant? NO

Same volume (size)
Density may be different, so masses are
different Venus (0.95 radius of earth, density
0.53)
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Acceleration due to Gravity (g)
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• The acceleration of a body arising from the
  earths gravitational pull.
• Units are ft/sec2 or m/sec2
• At the earths surface g is 9.8 m/sec2
• or
• 32 ft/sec2

(g) depends on position
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Acceleration due to Gravity (g)

• A body falling will continue to accelerate until
  air friction causes the body to reach a terminal
  velocity.

Acceleration due to gravity is independent of mass
F M A
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The Beam Balance and Weight
Known mass
unknown mass
1 kg
?
Gravity
Weight pull of gravity (a force)
Will it work everywhere? on Earth, another
planet? in space?
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Weight
M1M2
G
F
S2

• Weight is the force of gravity between me and the
  earth.
• 1. How can I reduce my weight?
• A) move scales to second floor?
• B) move to the mountains?

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Gravity and the Earth
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M1M2
G
F
S2
N
-Rotates west to east -Velocity greater at
equator, zero at poles -Centrifugal force bulges
earth at the equator
S
N
-So, the earth is slightly squashed at
equator -equator diameter is 42 km gt than pole
diameter
diameter
S