Download Newton`s Law of Universal Gravitation

Newton’s Law of Universal Gravitation

When an object
falls to earth (an
apple for example),
what shape path
does it appear
to take and why?

It is a common misconception
that astronauts in orbit are
weightless because they have
flown high enough to escape
the Earth's gravity. In fact, at
an altitude of 400 kilometres
(250 mi), equivalent to a
typical orbit of the Space
Shuttle, gravity is still nearly
90% as strong as at the
Earth's surface. Weightlessness
actually occurs because
orbiting objects are in free-fall
Gravitation

Every object with mass attracts every
other object with mass.

Newton realized that the force of attraction
between two massive objects:
Increases as the mass of the objects increases.
 Decreases as the distance between the objects
increases.

Law of Universal Gravitation
Mm

FG = G

G = Gravitational Constant



r2
G = 6.67x10-11 N*m2/kg2
M1 and M2 = the mass of two bodies
r = the distance between them
Law of Universal Gravitation

It is an inverse-square law:




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

If the distance doubles, the force drops to
1/4
If the distance triples, the force drops to
1/9
Distance increases by 10 = FG increasesb
by100
Other principles that follow inverse square laws:
Sound, light, electricity, magnetism and
Law of Universal Gravitation
Gravitational Force (N)
M1 and M2 = 10 kg
8E-11
7E-11
6E-11
5E-11
4E-11
3E-11
2E-11
1E-11
0
0
20
40
60
Distance (m)
80
100

What did you have to do differently to solve this
problem?
The Moon is attracted to the Earth. The mass of
the Earth is 6.0x1024 kg and the mass of the
Moon is 7.4x1022 kg. If the Earth and Moon are
345,000 km apart, what is the gravitational force
between them?
 FG = GM1M2 / r2

FG = (6.67x10-11 Nm2/kg2)
(6.0x1024 kg)(7.4x1022 kg)

FG = 2.49x1020 N
(3.45x108 m)2
Variations in Gravitational Field Strength


Strongest in red
Weakest in blue
Calculating g in the universe

Fg= GMm
r²
mg= GMm
r²
g= GM
r²
Calculating g in the universe



1) Using your new formula, calculate for
acceleration due to gravity on Earth
2 warm-ups
Ramifications of increased Fg1)strong
2) short
“
decreased Fg 1) tall
2) bones/muscles not as strong/atrophy
Warm up