Chapter 2: Part a Copernican Revolution

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Chapter 2 Part aCopernican Revolution
1.Newtons Three Laws 2. Gravitation 3.
Discovery of the outer Planets
Newton's marble tomb and monument in Westminster
Abbey
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Born in England on Christmas day 1643. Bubonic
Plague 1665 While home for 2 years with nothing
to do he made his most profound discoveries and
proposed his most startling theories.
Isaac Newton (1643 - 1727))

• Invented calculus to solve mathematical problems
  related to motion
• Discovered the three laws of motion
• Discovered the universal law of gravitation

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Sir Edmond Halley (1656 - 1742) English
astronomer known for his study of comets, noticed
that the comets of 1531, 1607, and 1682 seemed
similar hypothesized that they were the same
comet and predicted the comet would return in
1758 when it was observed as predicted, the
comet was named Halley's Comet in his honor.
1684 Newton was in a discussion with Edmund
Halley, when Halley remarked But why do planets
move the way they do? Newton astounded everyone
with the answers from his work 20 years earlier.
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Newtons Three Law of Motion
1687

• An object at rest tends to stay at rest, and an
  object in uniform motion tends to remain in that
  state of motion, unless an external force is
  applied to it (the Law of Inertia).
• A force causes acceleration (a change in the
  velocity) of an object (Fma).
• For every action there is an equal and opposite
  reaction.

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Newtons First Law of Motion An object
continues in a state of rest or in a state of
uniform motion at a constant speed along a
straight line unless compelled to change that
state by a net force.
An astronaut floating in space will continue to
float forever in a straight line unless some
external force is accelerating him/her.
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Newtons 2nd Law of Motion
The amount of acceleration (a) produced by a
force (F) depends on the mass (m) of the object
being accelerated.
F m a
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Newtons Third Laws of Motion
For every action, there is an equal and opposite
reaction.
The same force that is accelerating the boy
forward is accelerating the skateboard backward.
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No Force
Force
Force
Force
Force of Gravity
Force
Moons Orbit
Force
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Newtons Law of Gravity 1686
Two bodies attract each other with a force that
is proportional to the mass of each body and
inversely proportional to the square of the
distance between them.
Wood from Newtons Apple Tree

• G is the gravitational constant
• d is the distance between the objects
• M1 and M2 are the masses

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Change of Gravity with distance
100 lb
1/4 (100 ) 25 lb
AST121,Fall 2005 Robert Zimmerman University of
Oregon
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The Acceleration of Gravity
The acceleration due to Earths gravity is g
10 m/s2

• As objects fall, they accelerate.
• The higher you drop the ball, the greater its
  velocity will be at impact.

Mercury 0.378 Venus 0.907 Earth
1.000 Mars 0.377 Jupiter 2.364
Saturn 0.916 Uranus 0.889
Neptune 1.125 Pluto 0.0675
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Escape Speed
how much speed an object needs to overcome
gravitational pull of gravity

• Moon 2.38 km/sec
• Mars 5 km/sec
• Earth 11.2 km/sec
• Jupiter 60 km/sec

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Types of Orbits
Planets
To help determine the paths of the planets and
the forces upon them, Newton needed a more
sophisticated mathematics than was then
available. So he invented calculus
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Meaning of Keplers 3rd Law and Gravity
M1M2a3/p2
Same value for all planets
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Binary Stars stars wobble due to the presence of
the other one.
The masses can be computed from measurements of
the orbital period (P) and orbital dimensions (a)
of the system
Center of Mass
M1M2a3/p2
Doesnt tell you what the individual masses of
the stars are-- only there sum. If you can also
measure the ratio of the distances from the two
stars to the center of mass then you get the
individual mass
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other planets discovered.
The year 1781 The first planet discovered.
William and Caroline Herschel
Uranus
The year 1846 First observed by Galle and
d'Arrest (based on calculations by Adams and Le
Verrier).
Neptune
Pluto
The year 1930 Discovered by Clyde Tombaugh
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Discovery of Uranus by Sir William Herschel
(1738-1822) Discovered Uranus on March 13, 1781

• Discovered accidentally while Herschel was
  surveying the stars. One "star" seemed different
  and within a year was shown to have a planetary
  orbit 18 times farther from the Sun than Earth.
• The new planet was named Uranus after the father
  of Saturn in Roman mythology.
• The planet had been observed numerous times by
  other astronomers as early as 1690, but it was
  thought to be another star.

Uranus was discovered using this 15-centimeter
(6-inch) telescope designed and built by Herschel.
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Discovery of Neptune 1846
Perturbation
Suns Gravity
Suns Gravity
J. C. Adams of Britain and U. J. Leverrier of
France independently predicted the position of
Neptune it was discovered by J. C. Galle in
1846, the day after he received Leverrier's
prediction.
Neptunes Gravity
Discovered as the result of irregularities in the
motion of Uranus and was the first planet to be
discovered on the basis of theoretical
calculations.
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Pluto Discovered 1930 by C. Tombaugh.
Clyde W. Tombaugh 1906-1997
First proposed by Percival Lowell on the
perturbations in the orbit of Uranus. He began
searching for the planet in 1905. Independent
calculations were published by W. H. Pickering
and others. In 1929, the search for a new
planet was resumed at Lowell Observatory. On
Feb. 18, 1930, Clyde W. Tombaugh discovered a
trans-Neptunian planet. Pluto is named for
the mythical Greek god of the underworld
First two letters of Pluto stand for Percival
Lowell
Lowell's calculations now appear to have been
incorrect and predicted location was accidentally
accurate---Pluto is far too small to have
detectable influence on Neptune or Uranus
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launched in March of 2002, the GRACE mission is
mapping variations in the Earth's gravity field
over its 5-year lifetime.
The GRACE mission has two identical spacecrafts
flying about 220 kilometers apart in a polar
orbit 500 kilometers above the Earth.

• GRACE maps the Earth's gravity fields by
  making measurements of the distance between the
  two satellites, using GPS and a microwave ranging
  system.
• The gravity variations include
• changes due to surface and deep currents in the
  ocean
• runoff and ground water storage on land masses
• exchanges between glaciers and the oceans
• variations of mass within the Earth

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Gravitational Slingshots
The gravitational slingshot maneuver was used
was in the 1970's, when the spacecrafts to
Jupiter used multiple gravity assist flybys of
the aligned planets Jupiter, Saturn, Uranus and
Neptune, to boost the spacecraft beyond the gas
giants.
1.Sept 5, 1977 2. Aug 20, 1977
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An orbit can change if it gains or loses energy
from another object, such as a gravitational
encounter. Jupiter can capture comets or eject
them from the inner solar system.
Ejections of Comets
Capture of Comets
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End of Chapter 2bThe Copernican Revolution
Go to Chapter 6
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Born in England on Christmas day 1643. Bubonic
Plague 1665
Isaac Newton (1643 - 1727))
1668 Invented the reflecting telescope
http//www.pbs.org/wgbh/nova/newton/einstein.html
Edmond Halley (right) had no idea when he visited
Newton with a simple question in August 1684 that
it would lead to what many consider the greatest
work of science ever written.
Though he made his experiments on light as early
as 1666, when he was only 24 years old, he didn't
publish his classic Opticks, which summarized his
findings on light and color, until 1704
Discovered calculus
"Newton," painted by William Blake in 1795
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