FAQ/Gravity/en
What about gravity?
According to the wikipedia
In geodesy and geophysics, theoretical gravity or normal gravity is an approximation of the true gravity on Earth's surface by means of a mathematical model representing Earth. The most common model of a smoothed Earth is a rotating Earth ellipsoid of revolution (i.e., a spheroid).
g = g45 = 9.80665 m/s2 (32.1740 ft/s2) based upon data from World Geodetic System 1984 (WGS-84), where g is understood to be pointing 'down' in the local frame of reference.
The standard acceleration of gravity or standard acceleration of free fall, often called simply standard gravity and denoted by ɡ0 or ɡn, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is a constant defined by standard as 9.80665 m/s2 (about 32.17405 ft/s2). This value was established by the 3rd General Conference on Weights and Measures (1901, CR 70) and used to define the standard weight of an object as the product of its mass and this nominal acceleration.
For the mass attraction effect by itself, the gravitational acceleration at the equator is about 0.18% less than that at the poles due to being located farther from the mass center. When the rotational component is included (as above), the gravity at the equator is about 0.53% less than that at the poles, with gravity at the poles being unaffected by the rotation. So the rotational component of change due to latitude (0.35%) is about twice as significant as the mass attraction change due to latitude (0.18%), but both reduce strength of gravity at the equator as compared to gravity at the poles.
Note that for satellites, orbits are "decoupled" from the rotation of the Earth so the orbital period is not necessarily one day, but also that errors can accumulate over multiple orbits so that accuracy is important. For such problems, the rotation of the Earth would be immaterial unless variations with longitude are modeled. Also, the variation in gravity with altitude becomes important, especially for highly elliptical orbits.
The Earth Gravitational Model 1996 (EGM96) contains 130,676 coefficients that refine the model of the Earth's gravitational field. The most significant correction term is about two orders of magnitude more significant than the next largest term. That coefficient is referred to as the J2 term, and accounts for the flattening of the poles, or the oblateness, of the Earth. (A shape elongated on its axis of symmetry, like an American football, would be called prolate.) A gravitational potential function can be written for the change in potential energy for a unit mass that is brought from infinity into proximity to the Earth. Taking partial derivatives of that function with respect to a coordinate system will then resolve the directional components of the gravitational acceleration vector, as a function of location. The component due to the Earth's rotation can then be included, if appropriate, based on a sidereal day relative to the stars (≈366.24 days/year) rather than on a solar day (≈365.24 days/year). That component is perpendicular to the axis of rotation rather than to the surface of the Earth.
Various, successively more refined, formulas for computing the theoretical gravity are referred to as the International Gravity Formula, the first of which was proposed in 1930 by the International Association of Geodesy.
Some of the various formulas used to calculate "gravity" are:
- Somigliana equation (1980)
- International gravity formula (1930)
- International gravity formula (1967)
- International gravity formula (1980)
- Cassinis (accounting for height dependence)
- WELMEC formula
Their model also require the "gravity anomaly", which is at a certain location on the Earth's surface, there is a difference between the observed value of gravity and the value predicted by a theoretical model. If the Earth were an ideal oblate spheroid of uniform density, then the gravity measured at every point on its surface would be given precisely by a simple algebraic expression. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. The theoretical value of gravity can be corrected for altitude and the effects of nearby terrain, but it usually still differs slightly from the measured value. This gravity anomaly can reveal the presence of subsurface structures of unusual density. For example, a mass of dense ore below the surface will give a positive anomaly due to the increased gravitational attraction of the ore.
Gravity on a flat earth?
Despite all the mathematical models and theories needed to make their heliocentric model work, Gravity on a flat earth can be explained by buoyancy, density, pressure and electromagnetism.
Buoyancy and density
Things fall at different speeds depending on how dense it is. If you drop a ball in water it falls slower than if you drop in low altitude air. High altitude air, the ball falls faster. It depends on density.
Electromagnetism
Considering we have a giant magnetic field around us, that can account for up and down. There is many misunderstood effects of magnets such as the Lenz effect, and other magnetic miracles. In fact, extremely powerful magnets can effect nonmagnetic objects. There is a video on the internet of a powerful magnet from a laboratory levitating a strawberry.[1]
So if we already have magnetism, why do we need another force? Isaac Newton's "Gravity" is the only force of nature not found on the electromagnetic spectrum. Sound, light, radio, everything can be measured on the spectrum except gravity; That should tell you already there is a problem with the theory.
Pressure mediation
Also, air pressure can cause a directional force. When you put air in a container and apply pressure, it can cause things to move in the direction of the pressure. Temperature and expansion of molecules can add to the force of pressure since heated molecules get excited and knock into each other from vibrations causing them to expand.
Mass attracting mass?
Gravity is never, ever seen lab experiments not even in micro levels. Dust and bacteria or proteins are not attracted to large boulders because of gravity so why would something attract another thing by its mass alone? Gravity is used to conveniently dismiss all logical arguments against a ball. Why does the moon go around the earth and not get pulled away by the sun? Gravity. Why does the air move perfectly with the earths spin giving no evidence we are spinning? Gravity. In fact, Stephen Hawking said "because there is a force such as gravity the universe can and will create itself from nothing".
It gets pretty stupid, you get the idea, gravity has almost become the new religion. Electromagnetism has proven its ability to cause a directional force! Why would people not assume that electromagnetism is causing the up/down force to the earth? Especially when we already have a magnetic field that can be confirmed with a compass? You would think every scientist would run to the North Pole to test the power of its magnetic field.