Gravitation : Mechanics
Gravitation (or gravity) is a phenomenon by which objects with mass of any size
are pulled towards each other.
In modern physics, the theory of general relativity ascribes gravity to the curvature
of the 4-dimensional space-time rather than it being a force. Instead, force is
treated by means of geometry, for which the geometry is described by mathematical
metric tensors. The curved space is caused by the mass of the object, in a similar
manner in which a large bowling ball distorts the surface of a trampoline. Using
a planetary scale to illustrate, a second smaller object that succumbs to the effect
of gravity, free-falls with inertial motion towards the larger object and in fact,
both objects accelerate relative to each other. The second object follows a path
along the curved space in a similar manner that a marble which is tossed towards
the bowling ball on the trampoline would encircle it, or its trajectory becomes
deflected and continues beyond.
In the classical physics of Newton, gravity is a force, being the weakest of the
four fundamental forces. Newton's theory simplifies gravity into what we see in
everyday life as it giving weight to objects with mass, keeping the planets in orbit
around the Sun, causing the tides of the oceans by the moon, and many other phenomena,
including forming stars and galaxies from clusters of matter. It is worth pointing
out that acceleration under Newton's theory cannot occur if a force has not been
applied while general relativity allows such acceleration, even if it is in a relative
sense between two objects.
The gravitational inverse-square force law of Newton provides practical approximations
when speeds and gravitational fields are low, as observed in everyday activity on
Earth. General relativity encompasses these approximations in addition to relativistic
calculations such as those involving black holes or adjustments to the clocks on
satellites and their position due to their high orbiting speed around Earth.
F = G m1 m2
r 2
where m1 and m2 are the masses
of two attracting bodies, r is the distance between them and G
is a physical constant known as the gravitational constant given by
G
= 6.67 x 10-11 m3 kg-1 s-2
Full Definition
Published on: 25 Sep 2017 at 0843.
Last updated: 26 Sep 2017 at 1020.