# Gravitics [Gravity Studies]

Principia - 1687
Isaac Newton
[Newton is said to have discovered the force of gravity
when he saw an apple falling from a tree. However others such
as Galileo and Cavendish might have been conducting their own
experiments with gravity before Newton.]

- gravity as a force that obeys an inverse square law. >
General Theory of Relativity - 1915
Albert Einstein

This theory treats gravity as a consequence of the geometry of space.
A mathematical construct called "space-time" is used in this theory.
This theory tries to suggest that gravity is not a real force.
Newtons 1st law says that objects travel in straight lines or are at a rest.
[Newtons first law is sometimes described as: an object travelling under
its own inertia in a straight line, or an object remaining at rest because
of its inertia against motion. Newtons first law describes a "straight inertial path".]
Einstein's theory suggests that large masses create "curved inertial paths" in space.
So objects travel in curves, or travel in orbits under their own
inertia, when they are near a large mass.

Quantum Theories of Gravity - 1950s - present.
Various Scientists

These theories postulate that gravity might be associated with a
fundamental particle such as a "Graviton" . These theories are very
difficult to test because gravity is a very long range, very weak force,
compared to the other forces of nature. Quantum theories are on a
very small scale and they are trying to describe
a force that acts over very large distances.
[quantum theories of gravity are probably
often connected to "Unified field theories"
andn"String Theories".]

Theories before Newton/Cavendish.
1)Ptolemy - Geocentric solar system. This theory is wrong! But
it can predict planetary motions quite accurately. Epicycles
2)Aristotle - Heavier masses fall faster under gravity.This is wrong!
3)Copernicus - Heliocentric solar system.
4)Tycho Brahe - collected much information about planetary motion.
5)Johannes Kepler - 3 laws of planetary motion.
- Planets travel in ellipes not circles.
6)Galileo - Different masses fall at the same rate .Periodic motion of objects under gravity.

Gravitational Machines.

1. Inclined plane - reducing the gravitational force by
building an inclined plane.The plane provides a "normal" force.
The inclined plane is a way of moving a mass upward against a
reduced force of gravity. The reduced gravity acts
downward parallel to the plane.

2. Weights and Pulleys - masses changing elevation in a gravitational field.

3 Water Wheels. [They are a reverse of windmills.]- water flowing down rivers.

4. Hydroelectric Dams - water flowing water down rivers.

5. Tidal power stations - sea water changing elevation because of the moon's gravity.
Information

Gravitational Systems.
[Systems where there are significant gravitational Fields
and masses that can move under gravity.]

gravitational machines can be built where there exists a "gravitational system".
A gravitational system exists where there are one or more very large masses that
produce a significant gravitational field.

Examples of gravitational systems are:
- The solar system
. - The earth and the moon.
- The surface of the earth and small "weights" above the surface.

[This webpage is under construction.