Physics of Gravity and Free Fall: "The Microgravity Demonstrator" 1998 NASA

more at http://quickfound.net/

'The Microgravity Demonstrator is a tool used to create microgravity conditions in the classroom. A series of demonstrations is used

to provide a dramatically visual, physical connection between free-fall and microgravity conditions in order to understand why various types of experiments are performed under microgravity conditions.'

Originally a public domain film from  NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Micro-g_environment

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

The term micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous with the terms weightlessness and zero-g, but indicates that g-forces are never exactly zero—just very small (on the ISS, for example, the small g-forces come from tidal effects, gravity from objects other than the Earth (such as astronauts, the spacecraft, and the Sun), and, occasionally, air resistance). The symbol for microgravity, μg, was used on the insignias of Space Shuttle flights STS-87 and STS-107, because these flights were devoted to microgravity research in low Earth orbit...

A "stationary" micro-g environment would require travelling far enough into deep space so as to reduce the effect of gravity by attenuation to almost zero. This is the simplest in conception but requires travelling an enormous distance, rendering it highly impractical. For example, to reduce the gravity of the Earth by a factor of one million, one needs to be at a distance of 6 million kilometres from the Earth, but to reduce the gravity of the Sun to this amount, one has to be at a distance of 3.7 billion kilometres. (On Earth the gravity due to the rest of the Milky Way is already attenuated by a factor greater than one million, so we do not need to move away further from its center). Thus it is not impossible, but it has only been achieved so far by four interstellar probes (Voyager 1 and 2 of the Voyager program, and Pioneer 10 and 11 of the Pioneer program) and they did not return to Earth. If travel at the speed of light were possible for a spacecraft, it would take roughly three and a half hours to reach this micro-gravity environment (a region of space where the acceleration due to gravity is one-millionth of that experienced on the Earth's surface). To reduce the gravity to one-thousandth of that on Earth's surface, one needs to be at a distance of 200,000 km.

At a distance relatively close to Earth (less than 3000 km), gravity is only slightly reduced. As an object orbits a body such as the Earth, gravity is still attracting objects towards the Earth and the object is accelerated downward at almost 1g. Because the objects are typically moving laterally with respect to the surface at such immense speeds, the object will not lose altitude because of the curvature of the Earth. When viewed from an orbiting observer, other close objects in space appear to be floating because everything is being pulled towards Earth at the same speed, but also moving forward as the Earth's surface "falls" away below. All these objects are in free fall, not zero gravity.

Compare the gravitational potential at some of these locations.

Free fall

What remains is a micro-g environment moving in free fall, i.e. there are no forces other than gravity acting on the people or objects in this environment. To prevent air drag making the free fall less perfect, objects and people can free-fall in a capsule that itself, while not necessarily in free fall, is accelerated as in free fall. This can be done by applying a force to compensate for air drag. Alternatively free fall can be carried out in space, or in a vacuum tower or shaft.

Two cases can be distinguished: Temporary micro-g, where after some time the Earth's surface is or would be reached, and indefinite micro-g.

A temporary micro-g environment exists in a drop tube (in a tower or shaft), a sub-orbital spaceflight, e.g. with a sounding rocket, and in an airplane such as used by NASA's Reduced Gravity Research Program, aka the Vomit Comet, and by the Zero Gravity Corporation. A temporary micro-g environment is applied for training of astronauts, for some experiments, for filming movies, and for recreational purposes...