Question:
What is gravity?
Answer:
Gravity is the force of attraction between two bodies.
Question:
How is the force of gravity between two bodies determined?
Answered:
Newton’s equation for the force (in units of “Newtons”) of gravity between two objects is:
F = G x m1 x m2/d2
m1 and m2 are masses (in kilograms) and d2 is the distance (in meters) squared between the centers of the two objects. G is a constant, the gravitational constant, which is 6.67 x 10-11 when these units are used. The constant is a very small number, thus gravity is a very weak force in comparison to other forces. You notice the force of gravity only if a very large mass, such as Earth, is involved.
Question:
What is the force of attraction between a person with a mass of 63.5 Kg and Earth, with a mass of
5.95 x 1024 kg and a radius of 6.378 x 106 m?
Fact: G = 6.67 x 10-11 mkg/sec2
F = G x m1 x m2/d2
F = (6.67 x 10-11 mkg/sec2) (5.95 x 1024 kg)(63.5 kg)
—————————————
(6.378 x 106 m)2
F = 6.20 x 102 kgm/sec2
= 6.20 x 102 N
Question:
What is gravitational acceleration?
Answer:
Gravitational acceleration is the rate at which the attractive force of gravity accelerates a body. On Earth, this is 9.8 m/sec2.
Question:
How is the gravitational acceleration (g) of a body on Earth calculated?
Answer:
g = G x M/d2
G = Newton’s constant
M= mass of Earth
d = radius of Earth (distance from Earth’s center to the object)
g = (6.67 x 10-11 mkg/sec2) (5.95 x 1024 kg)
————————————— —- = 9.8 m/sec2
(6.378 x 106 m)2
FYI: This means that the force of attraction, which the weight of an object, can be calculated using this equation:
F = m g (g is the gravitational attraction toward an object. The value for Earth = 9.8 m/sec2)
If I redo the equation for the moon, replacing the earth’s mass and radius with that of the moon, I get:
F = 103 N
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