‘Gravity is the Force that appears to attract Physical Bodies towards each other’.
Let’s see how much we know about it.
Note the Definition, ‘appears to attract’ – We are not sure.
Einstein’s Views -‘Theory of General Relativity‘ as applied to Gravity.
Space and Time , Spacetime condition Gravity.
“General relativity, or the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1916[1] and the current description of gravitation in modern physics. General relativity generalises special relativity and Newton’s law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.”…
Some predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, and the gravitational time delay. The predictions of general relativity have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.
(wiki)
Space is curved(please read my blogs under Astrophysics).
Have we defined Space, Tie?
No.
Consequently Gravitation as influenced by Spacetime,at best, remains a conjecture.
Newton on Gravity(theory discared, yet being used in Calculations)
” “I deduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force 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’…
Although Newton’s theory has been superseded, most modern non-relativistic gravitational calculations are still made using Newton’s theory because it is a much simpler theory to work with than general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.’
Irrespective of the fact whether our Theory is Right or Wrong, Principles of Nature work,so much for Science.
By the way , can some one forward me the exact definition of Nature?
Earth’s Gravity.
a) Earth is ‘assumed’ to be surrounded by its own Gravitational Filed, which exerts an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point is proportional to the planetary body’s mass and inversely proportional to the square of the distance from the center of the body….
The fundamental is an Assumption.
Again, ‘ This means that, ignoring air resistance, an object falling freely near the Earth’s surface increases its velocity by 9.81 m/s (32.2 ft/s or 22 mph) for each second of its descent. Thus, an object starting from rest will attain a velocity of 9.81 m/s (32.2 ft/s) after one second, 19.62 m/s (64.4 ft/s) after two seconds, and so on, adding 9.81 m/s (32.2 ft/s) to each resulting velocity. Also, again ignoring air resistance, any and all objects, when dropped from the same height, will hit the ground at the same time.
Assumptions.
‘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, is approximately expressed below as thestandard average.
g = 9.81 m/s2 = 32.2 ft/s2′
We want to know Earth’s Gravitation, that is what we want to prove.
Acceleration of Bodies is determined the force of Gravitation.
So when we rely on the Acceleration of Objects under the influence of the Earths’ gravitation , have we not already assumed Earth’s Gravity?
We also ignore the effect of Electromagnetism and other forces at work,EM being dependent on Gravitation or is the other way around?
The Theory is riddled with Assumptions and leaping to conclusions.
http://en.wikipedia.org/wiki/Gravitation#Newton.27s_theory_of_gravitation
Chinese Scientists have found a way to measure Gravity and it throws Spanner in the works.
‘By conducting six observations of total and annular solar eclipses, as well as Earth tides, a team headed by Tang Keyun, a researcher with the Institute of Geology and Geophysics under the Chinese Academy of Sciences (CAS), found that the Newtonian Earth tide formula includes a factor related to the propagation of gravity.
“Earth tide” refers to a small change in the Earth’s surface caused by the gravity of the moon and sun.
Based on the data, the team, with the participation of the China Earthquake Administration and the University of the CAS, found that gravitational force released from the sun and gravitational force recorded at ground stations on Earth did not travel at the same speed, with the time difference exactly the same as the time it takes for light to travel from the sun to observation stations on Earth.
[…] By applying the new data to the propagation equation of gravity, the team found that the speed of gravity is about 0.93 to 1.05 times the speed of light with a relative error of about 5 percent, providing the first set of strong evidence showing that gravity travels at the speed of light.”
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