Near Earth's surface, the gravity or gravity acceleration is approximately 9.81 m/s^2.
That's a good question. There is no such thing as zero gravity in space. Gravity is everywhere in the universe and manifests itself in black holes, celestial orbits, ocean tides, and even our own weight. Gravity, however, does become weaker with distance. It is possible for a spacecraft to go far enough from Earth that a person inside would feel very little gravity. But this is not why things float on a spacecraft in orbit.
Things float on a spacecraft in orbit because they are in free fall. In a vacuum, gravity causes all objects to fall at the same rate. The mass of the object does not matter. If a person drops a hammer and a feather, air will make the feather fall more slowly. But if there were no air, they would fall at the same acceleration. That is what happens in a spacecraft. The spacecraft, its crew and any objects aboard are all falling toward but around Earth. Since they are all falling together, the crew and objects appear to float when compared with the spacecraft.
This condition of apparent weightlessness is called microgravity. Microgravity can be experienced in other ways, as well. For example, on reduced-gravity flights, airplanes fly in large arcs called parabolas. During the downward part of each arc, the passengers experience microgravity for about 20 seconds. Astronauts also train in these flights to prepare for space missions.
Microgravity affects the human body in several ways. For example, muscles and bones can become weaker without gravity making them work as hard. Astronauts who live on the space station spend months in microgravity and have to exercise regularly to maintain their health.
A small body in free fall will see zero gravity, since matter is entrained by the ether. ("Ether tells matter how to move".) So zero gravity from distant bodies.
A large body will see the gravity that the body in itself has generated. This gravity is caused by an ether wind blowing in radial direction.
With best regards from________________ John-Erik
Nothing in the universe is working with pull/push force. Newtonian gravity or velocity of mass does not make gravity, gravity is a natural phenomenon. Article Earth Gravity is not Newtonian
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The gravitational potential fills all of space. The earth, sun, moon, planets all have their own potential that adds to this. The total potential from all masses in the universe adds to roughly c^2 = (2.99792458E8 meters/second)^2 = 8.98755179E16 Joules/Kilogram.
To get the gravitational acceleration for anywhere on earth, you take the spherical harmonic model for the earth's gravitational potential and differentiate it. In words, "take the gradient of the gravitational potential". That gives an acceleration. Check the units and dimensions. The gradient operator itself has units of (1/Meters) or Meters^-1.
[ Grad ] * [ GravitationalPotential ] = [ meter^-1] * [ meter^2/second^2 ]
which yields [meters/second^2] which is acceleration.
The potential around the earth is not constant. It is pretty stable. If you check the International Centre for Global Earth Models (ICGEM) the current temporal models are 2160x2160 and updated once each month. But every moment new updates to the potential are changing the accelerations at the earth.
The sun and moon vector tidal signal is stable and easy to measure. It is the signal picked up by the network of superconducting gravimeters. There are better and low cost instruments now. There are MEMS gravimeters that are basically cell phone MEMS accelerometers that have been upgraded to be sensitive enough to track the sun and moon tidal signal.
When things happen on the sun, or as it moves relative to earth the change in the potential diffuses at the speed of light, updates the earth potential which is already here, and the acceleration signal from the sun only matches the earth based detectors, if you allow for the finite speed of the gravitational potential. For frequencies faster than about 40 samples per second, the spatial resolution is smaller than the earth. So if you want to use gravitational signals for imaging something that is 1 km, you need to use gravimeters that can operate faster than (2.99792458E8 meters/second)/(1000 meters) = 299,792.458 SamplesPerSecond about 300 Ksps. It is hard, but not impossible. I am looking at detectors that can work at 100 GigaSamplesPer Second (100 Gsps).
The gravitational field is not difficult to understand but it does require considerable effort. I recommend you decide what you want to do with it, then work hard on that. If you try to look at the whole of it, that will take you decades of very hard work. Learn Python, find the data and models, use the best that you can find, and do not waste time on freshman arguments.
To answer your question. Satellites in orbit, the centrifugal acceleration balances the gravitational acceleration so that orbit is stable, not growing or shrinking. That gives a "microgravity" environment where the average accerlation is zero, but there are still variations at about the "micro-g" level about 9.8E-6 meters/second^2. It is possible to create acceleration fields using accoustic, magnetic and electromagnetic fields to measure and balance the external gravitational potential and its gradients. This is not hard, just requires care and effort, fast sensors and computers.
I follow the micro and nanogravity groups. They want to create nanogravity fields on earth to simulate and benefit from zero accelerations. And they want to make synthetic acceleration fields for people living in orbit, taking long trips to Mars and back, and even ones living in orbit long term around Mars and Moon, even Venus and other places. For the Internet Foundation I put all of those kinds of things into a new field, "gravitational engineering" that gets things done, builds measures and tests.
I encourage you to look at what is going on and try to write it down. Not just talk, but do.
You might want to start with the mass of what you want to hold steady. If you have a kilogram mass on the earth and want to keep it levitated with fields, you have to provide the proper power, energy density, gradients and timings - so you do not damage anything. I am working out the power and field requirements to replace the whole first ("booster") stage for the SpaceX Starship. Rather than using all the chemical fuel, carefully and powerfully lift and accelerate the second stage to height and velocity it needs to begin its mission. That takes about 36 GigaWatts of power for several minutes. Not impossible even with todays methods. But I do it to check the planning and collaboration process when people from all countries and backgrounds work with "global open collaborative worksites" on interesting and challenging problems that require complete and precise models and verification.
Best wishes.
Richard Collins, The Internet Foundation