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New Physics
Old Physics
Aristotle’s Kinematics
(science of motion)
• Each element had a natural place in the Universe
and moved toward that natural place
• Earth and Water – moved down
• Air and fire – moved up
• Aether moved in circles because circle was
perfect.
• Natural motion- see above
• Violent motion- requires force F= mv
• Objects fall with a velocity proportion to their
weight.
• Laws of motion on earth are different from laws
of motion in the heavens.
Aristotle’s Cosmology
• Cosmology= study of the cosmos (universe)
• The earth is the center of the universe
• Planets, sun and moon revolve around the
earth.
• Stars and planets are fixed to a “crystal
sphere” which rotates around the earth.
• Celestial objects (sun, moon, planets, stars)
are perfect and immutable (ie no change)
Arguments against moving earth.
Practical
• Earth Circumference = 24,000 miles
• Rotates in 24 hrs
• Speed = 24,000/24= 1000 mph= 1500 ft/sec
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Earth’s orbit r= 93,000,000 miles
Circumference of orbit = 2πr = 580,000,000 miles
Revolves in 1 year =
365.25 days/year x 24 hr/day x 3600 s/hr= 30,000,000s
speed = 580,000,000 miles/ 30,000,000s = 19 miles/s
Birds in Trees
Children Jumping
• Imagine a bird sitting on the limb of a tree,
spots a worm on the ground and flies down to
eat the worm.
• In one second, the worm is 19 miles away.
• If a child jumped up while playing, the earth
would move under the child so the child
would be hopelessly lost in the woods.
Brahe and Parallax
• Taco saw no parallax (shift of the apparent
position of stars at different times of year.
• He concluded either
– The earth stood still
– The stars were extremely far away
• He could not believe the stars were so far
away that parallax could not be observed so
he concluded the earth must stand still
Arguments against a moving earth.
Philosophical
• Rotating earth means every part of the earth
would be rotating.
• But the natural direction of motion of earth is in
a straight line down.
• Therefore rotation of earth would be a violent
motion requiring great force.
• Where does a force large enough to move earth
come from?
Arguments against a moving earth.
Religious
• Philosophy of Aristotle incorporated into Church
doctrine.
• Thought that Bible taught a stable earth – verses
about the foundations of the earth- perhaps.
• February 16, 1600, the Roman Catholic Church
executed Giordano Bruno for espousing the belief
that not only did the earth move, but also the sun
moved and the universe was infinite. He was a
heretic in many and different ways, not just
science.
Sir Isaac Newton
(1643-1727)
“If I have ever made any valuable discoveries, it has been
owing more to patient attention, than to any other
talent.”
-Sir Isaac Newton
Background
Sir Isaac Newton (1643-1727)
 English scientist and mathematician
 Philosophiae Naturalis Principia
Mathematica (mathematic principles of
natural philosophy)
 Newton’s Laws of Motion
 Law of Universal Gravitation
Newton
• Most of the ideas of Newton had been hinted
at by others.
• Newton synthesize and applied
• 3 Laws
• + Law of universal gravitation
• Alexander Pope
“Nature and Nature’s laws
lay hid in night;
God said, Let Newton be!
and all was light”
Newton’s First Law
Law of Inertia (first stated by Galileo)
• An object at rest will remain at rest unless it
experiences a net external force. An object in
motion will continue in motion at the same
speed and in the same straight-line direction
unless it experiences a net external force.
• Corollary: If either the magnitude or the
direction of the velocity of an object changes,
someone or something has exerted a net force
on the object.
We seldom experience inertia
Why?
Friction
Applied
Force
Friction Force
Newton’s Second Law of Motion
• The acceleration of an object is directly
proportional to the net resultant force acting
on the object and is inversely proportional to
the mass of the object. The direction of the
acceleration is in the direction of the net
resultant force.
F=ma
Newton’s 3rd Law
• When one object exerts a force on a second
object, the second object exerts a force on the
first object that is equal in strength and
opposite in direction.
• For every action force there is an equal and
opposite reaction force.
• The ladder law- if you jump off of a ladder the
ladder exerts a force that moves you but you
also exert a force on the ladder that may move
the ladder in the opposite direction.
Air Resistance
• Without air resistance, all objects
would fall with the same
acceleration.
• The acceleration of gravity
• g = 9.8 m/s2
• Feather and ball -
In a vacuum
Projectile Motion
Parabolic Motion
Motion in a Circle
Motion in a Circle
Centripetal Force/Acceleration
v1
Fcenter
v2
Source of Centripetal Force
Gravity
Gravity
• A fundamental characteristic of all matter.
• Anything that has mass is attracted by the
force of gravity.
• Anything that has mass attracts other things
that have mass.
FG = G m1m2
d2
G =6.67 X 10 -11N m2/kg2
Calculating
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G =6.67 X 10 -11N m2/kg2
mass of sun = 1.989 x 1030 Kg
mass of earth = 5.974 x 1024 Kg
Distance from earth to sun = 1.496 x 1011 m
FG = G m1m2 =
d2
Calculating “Weight”
• What is the force of gravity of the earth on a
1.0 kg mass?
• Given
– G =6.67 X 10 -11N m2/kg2
– mass of earth = 5.974 x 1024 Kg
– mass of object = 1.0 kg
– earth radius = 6.378 x 106 m
FG = G m1m2 =
d2
Solar System Measures
• Sun’s mass 1.989 X 1030 kg
• Earth’s mass 5.974 X 1024 kg
• Moon’s mass 7.349 X 1022 kg
• Earth Orbit 1.496 X 1011m
• Moon’s orbit 3.844 X 105 m
FG = G m1m2 =
d2
Newton’s Religion
• LORD’S PRAYER
• “Thy kingdom come on earth as it is in heaven.
• The same laws of motion that we observe on earth
are the same laws of motion we observe in the
heavens affecting the planets and stars.
Newton and the
Copernican Revolution
• Why the bird can catch the worm and why the
child does not get lost in the woods
– Inertia
• Straight line, parabolic and circular motion
• Gravity
– Force that holds moon to the earth
– Force that holds planets in elliptical orbits
Newton’s Contribution
• Solidified the “Copernican” Revolution
• Studied Light and formulated the
“corpuscular” theory of light that held sway
for 250 years.
• Director of the Mint – for this he was knighted
• Commentary on the book of Revelation was
his proudest contribution.