Theories of Gravitation

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Theories of Gravitation

• PHYS 001 Section 001
• Project 1
• By
• Chi Pang Chan
• King Ho Fung
• Sinhaar Joshua Rodrigues

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Contents

• Introduction
• Discovery of Gravitation
• The Micro-view Macro-effect of Gravitation
• Future Trends of Gravitation

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Introduction

• Why astronaut can float, but we cant?
• When Armstrong returned to the earth, why he
  could not float again?
• Key Gravitation, the invisible force!!

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No ideas of Whats up?

• So what is gravitation, or gravity? The simplest
  definition of gravity is the tendency of masses
  to move toward each other.
• And now, before looking into the force, we should
  have a view our brilliant history of
  gravity-discovering.

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Discovery of Gravitation

• 4, 000 years ago, ancient astronomers had already
  identified five of our solar system's planets.
  However, people did not even know the existence
  of gravity. Many thinkers suggested there some
  mystical heavenly power drove the movement of
  these planets, not the force that we experience
  on Earth.

• Years later, Greek philosopher, Aristole(384
  BC-322 BC), suggested the idea of geocentric
  universe which believed earth was the centre of
  the universe.
• He also said heavier objects fall faster than
  light ones because of so called "natural"
  motions
• These idea involved too much thinking but too
  few facts that left many questions with the
  geocentric view.

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• The man on the left is Claudius Ptolemy, a Greek
  astronomer, who embodied geocentric universe into
  a model called Ptolemy's model of the universe.
• Ptolemy could not give a good, scientific
  explanation as to what actually caused the
  planets to move.

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• The ideal of geocentric universe was challenged
  by Nicolas Copernicus, an astronomer.
• He suggested that the Earth is actually orbiting
  around the Sun with other planets, now known as
  Copernican revolution. This audacious step for
  scientific thinking met by many strong
  oppositions, especially from the Catholic church.

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• Galileo Galilei, an Italian, was a proponent of
  Copernicus.
• Galileo changed people's mossy mind through
  scientific means. He threw a large and small
  weight down the Leaning Tower of Pisa and found
  out two weight reached the ground at the same
  time. Aristotle believed that heavier objects
  fell faster than the lighters.
• His use of experiment evidence is critical in
  science development
• Galileo also invented telescope, through which he
  discovered lunar craters, moons around Jupiter,
  the rings of Saturn and sunspots.

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• Johannes Kepler,a German , picked up the data
  from his employer, Tycho Brahe and formulated the
  three Kepler's Laws, a set of simple empirical
  theories.
• Keplers Law estimates that planets are actually
  moving in eliptical paths around the sun.

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• Sir Isaac Newton, an English, who set the
  foundations for modern physics. Many of his
  discoveries and theories in the areas of light,
  color, and optics form the basis for current
  scientific thought in these disciplines.

• A falling apple to Newtons head triggered his
  interests in gravitation. He used Keplers laws
  and his observations the law of universal
  gravitation.
• The law states the earths gravity was
  responsible for keeping the moon in orbit and
  that the Suns gravity was responsible for
  keeping the planets in orbit.
• Newtons other significant contributions includes
  the Calculus and the Laws of Motion.

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• Newtons Law of Universal Gravitation was widely
  adopted at the time. However, it only fails to
  predict the orbit of Mercury.
• However, the small flaw has not been longer a
  problem since the rise of Albert Einstein.

• The German declared the General Relativity which
  is an innovative idea that we are living in a
  four dimensional universe called space-time.
• General Relatively has completely changed our
  precedent ideas and understanding of the universe
  !
• General Relativity soon replaced Newtons law of
  universal gravitation as the official explanation
  of gravity.
• Nowadays, Newtons law is till used for
  educational purpose because of its
  easy-to-understand advantage.

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The Micro-view

• What is Gravitation?
• Gravitation (or gravity) is a force of
  attraction.
• All pieces of matter in the universe produce
  gravitation, therefore it is also called a
  universal force.Even a pencil or yourself
  generate gravitation.
• It pulls on every pieces of matter in the
  universe regardless of their sizes or types.
• Every object is surrounded by a gravitational
  field which pulls any other object inside that
  field towards it.

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A Special Force - Characteristics

• First, gravitation is always attractive. Other
  force like electromagnetism which can either be
  attractive or repulsive might cancel its
  strength out.
• Gravitation can act over huge distances.
  Comparing with nuclear force which can act only
  within atoms, gravity can attract planets in
  universe over extremely long distances.
• Despite gravitation can exist in long distances,
  it has the weakest strength among all other kinds
  of existing force. However ..

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Newtons Law of Universal Gravitation

• We just know that gravitation is the weakest
  force, then we might doubt how it can bind two
  huge planets together at a certain distance.The
  Law of Universal Gravitation explains this !From
  the equation shown above, - The force is
  directly proportional to the product of the two
  objects mass.- The force is inversely related
  to the square of distance between the two
  objects counting from their centers, no
  surfaces!
• Simply, The larger the mass of and distance
  between two objects, the greater the strength of
  gravitation between them.

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The Marco-effect

• Tides- caused by the gravitational pull of the
  Sun and Moon.
• - Moon orbits around the Earth ? sides of the
  Earth becomes closer nearer to Moon ?
  gravitational pull on the ocean towards the
  direction of moon.
• On the ocean, low tides are the compensation for
  the high tides.

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Future Trends of Gravitation

• The world is unpredictable. We only know a
  little.
• General relativity is a good theory but cannot
  last forever, similar to Newtons Law of
  Universal Gravitation.

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WHY?!

• Although gravity and structure of the universe
  are described in large scale
• However, the theory that we use to describe
  structures on a small scale contradict general
  relativity in certain ways.
• ?The two theories cannot both be right!!!

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Main Goal of Physics Today (Probably also the
Future ?)

• Combine general relativity and quantum mechanics
  into one grand, all scales unified theory
• Margin of Thought
• unification gravity with electromagnetism, strong
  and weak nuclear forces
• all four of these interactions are simply
  different aspects of a single force.
• ? Gravity is just one part of a larger force
  which is responsible for all the interactions
  between matter.

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However..

• Who knows?
• Only God and time can tell !!!
• Thank you for all of your attentions.

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Resources

• Chaisson-McMillian Astronomy A beginners
  Guide to the Universe
• http//micro.magnet.fsu.edu/optics/timeline/people
  /
• http//csep10.phys.utk.edu/astr162/lect/cosmology/
  gravity.html
• http//www.marsacademy.com/orbmect/orbles1.htm