2. GRAVITATION THEORY
• Gravitation or gravity is a natural phenomenon
by which all physical bodies attract each other.
It is experienced at the agent that gives
weight to objects with a mass which cause them
to fall when they are dropped.
• Gravitation is one of the four fundamental
interactions of nature, in modern Physics, the
phenomenon of gravitation is most accurately
described by the general theory of relativity by
Einstein. Einstein showed that gravitation was
not an attractive force, but a manifestation of
the distortion of the geometry of space-time
under the influence of objects that occupy it.
3. The Newton's law of universal
gravitation postulates the gravity force
proportional to masses of interacting
bodies and inversely proportional to the
square of the distance between them.
It provides an accurate approximation
for most of the physical situations.
4. From a cosmological perspective,
gravitation causes dispersed of
matter to coalesce, and coalesced
matter to remain it intact, this
explained the existence of planets,
stars, galaxies and most of the
macroscopic objects in the
universe..
5. Gravity is also important for some factors
of the Earth, it is responsible for keeping
the Earth and the other planets in their
orbits around the Sun, for keeping the
Moon in its orbit around the Earth, for the
formation of tides, for natural convection,
by which fluid flow occurs under the
influence of a density gradient and gravity,
for heating the interiors of forming stars
and planets to very high temperatures, and
for various other phenomena observed on
Earth and throughout the universe.
6. EARTH’S GRAVITY
• Every body (including the Earth) is surrounded by its own
gravitational field, which applies an attractive force on all
objects. The strength of this field is proportional to the
planetary body's mass and inversely proportional to the
square of the distance from the centre of the body.
• The strength of the gravitational field is numerically equal
to the acceleration of objects under its influence, and its
value at the Earth's surface, denoted g = 9.80665 m/s2 =
32.1740 ft/s2).
• This means that, without air resistance, an object falling
freely near the Earth's surface increases its velocity
9.80665 m/s. so an object starting from rest will gain a
velocity of 9.80665 m/s after one second and also all
objects, when dropped from the same height, will hit the
ground at the same time.
7. • According to Newton’s 3rd Law, the Earth also accelerates
towards the object until they collide. Because the mass of
the Earth is huge the acceleration imparted to the Earth
by this opposite force is very low in comparison to the
object ones.
• The force of gravity on Earth is the resultant of the sum
of two forces: (a) The gravitational attraction, and (b) the
centrifugal force. At the equator, the force of gravity is
the lowest due to the centrifugal force caused by the
Earth's rotation. The force of gravity varies with latitude
and becomes stronger as you increase in latitude toward
the poles. The standard value of 9.80665 m/s2 is the one
originally
8. GRAVITY AND ASTRONOMY
The discovery and application of Newton's law of gravity
accounts for the detailed information we have about the
planets in our solar system, the mass of the Sun, the
distance to stars, quasars and even the theory of dark
matter. Although we have not travelled to all the planets nor
to the Sun, we know their masses. These masses are
obtained by applying the laws of gravity to the measured
characteristics of the orbit. In space an object maintains
its orbit because of the force of gravity acting upon it.
Planets orbit stars, stars orbit Galactic Centres, galaxies
orbit a centre of mass in clusters, and clusters orbit in
super clusters. The force of gravity exerted on one object
by another is directly proportional to the product of those
objects' masses and inversely proportional to the square of
the distance between them.
9. ISAAC NEWTON
(25 December 1642 – 20 March
1727)
Isaac Newton was an English physicist and
mathematician who is Widely Regarded as one
of the Most Influential scientists of all time
and as a key figure in the scientific revolution.
His book, Philosophiæ Naturalis Principia
Mathematica (Mathematical Principles of
Natural Philosophy), first published in 1687,
laid the foundations for classical mechanics of
Most. Also Newton made seminal Contributions
to optics and shares credit with Gottfried
Leibniz for the invention of the infinitesimal
calculus.
10. NEWTON’S PRINCIPIA
Newton's Principia formulated the laws of
motion and universal gravitation That
Dominated scientists' view of the physical
universe for the next three centuries. It
Also Demonstrated That the motion of
objects on the Earth and of celestial
bodies That Could be Described by the
same principles. By Deriving Kepler's laws
of planetary motion from his mathematical
description of gravity, Newton removed
the last Doubts about the validity of the
heliocentric model of the cosmos.
11. REFLECTING TELESCOPE
Newton built the first practical reflecting
telescope and developed a theory of color
based on the observation that a prism
decomposes white light into the many colors of
the visible spectrum. He also formulated an
empirical law of cooling and studied the speed
of sound. In addition to his work on the
calculus, as a mathematician Newton
contributed to the study of power series,
generalized the binomial theorem to noninteger exponents, and developed Newton's
method for approximating the roots of a
function.
12. NEWTON’S THEORY OF
GRAVITATION
His book (Principia) hypothesizes the
inverse-square law of universal gravitation.
In his own words, “I deduced that the
forces which keep the planets in their orbs
must be reciprocally as the squares of
their distances requisite to keep the Moon
in her Orb with the force of gravity at the
surface of the Earth; and found them
answer pretty nearly. from the centers
about which they revolve: and thereby
compared the force.
13. Newton's theory enjoyed its
greatest success when it was used
to predict the existence of
Neptune based on motions of
Uranus that could not be accounted
for by the actions of the other
planets. Calculations by both John
Couch Adams and Urbain Le Verrier
predicted the general position of
the planet, and Le Verrier's
calculations are what led Johann
Gottfried Galle to the discovery of
Neptune.
14. A discrepancy in Mercury's orbit
pointed out flaws in Newton's theory.
By the end of the 19th century, it was
known that its orbit showed slight
perturbations that could not be
accounted for entirely under
Newton's theory, but all searches for
another perturbing body had been
fruitless. The issue was resolved in
1915 by Albert Einstein's new theory
of general relativity, which accounted
for the small discrepancy in
Mercury's orbit.
15. Although Newton's theory has
been superseded, most modern
non-relativistic gravitational
calculations are still made using
Newton's theory because it is a
much simpler theory to work with
than general relativity, and gives
sufficiently accurate results for
most applications involving
sufficiently small masses, speeds
and energies.
