As gravity is defined as a state in which either acts no gravity, or the impact is not felt. Since the range of gravity is in principle infinite, there is virtually no point in the universe where it does not work. However, there are states in which the effect of gravity is not noticeable, such as in a free fall in a vacuum, in a satellite or a parabolic flight. They are characterized by the fact that only gravity acts.


The effect of gravity on earth is evident, for example, the fact that an apple from the tree falls to the ground, or that we are pressed with our weight on the floor. The severity, we feel it and usually equate with gravity, so that, the opposing force of the soil does not affect all parts of our body evenly, but mostly on our feet. Therefore, our body is compressed slightly.

If other than the force of gravity do no other external forces, there is weightlessness. The easiest way to achieve weightlessness, is the free fall - but only for a limited time. A truly free fall is possible only if the air resistance is eliminated, which is achieved in evacuated drop towers.

As in the parabolic flight each perpendicular, oblique or horizontal body thrown or generally any body weightless on a parabolic trajectory ( without force, thus in particular no air friction). In so-called parabolic flights are similar to the air friction of an aircraft by the thrust of the engines or suitable maneuvers from the exact and accomplished so for a few seconds of weightlessness.

Enduring in weightlessness you are on the circular path of a space station around the Earth. Although in height, in which a space station is usually still work about 90% of Earth's gravity, it is not felt by the astronauts - because apart from the gravity accelerates all mass points equal to act, no other forces.

When simulating weightlessness under water as they also carried out for training for astronauts, however, there is no real weightlessness: While it is compensated gravity through the buoyancy in the water so that the astronauts float in the water. On every single atom but also acts gravitation. Only on average, the gravitational force is removed by pressure forces. It has therefore been in the water do not like the feeling of weightlessness in free fall. Rather, one feels carried by the water.

  • People in weightlessness

On board the ISS: Michael Foale trained on the treadmill, which hangs on the " ceiling".

Weightless astronaut in Earth orbit

Weightlessness during a parabolic flight in a Boeing C -135

Examples of ( approximate ) zero gravity in everyday life

  • In a jump on a trampoline of 1.5 meters height, the feeling of " weightlessness " are experienced for more than one second.
  • If a vessel thrown several meters, therein the items behave with each other virtually weightless. Examples: a large, empty plastic water bottle with a few thrown in nuts or murmur; a glued Plexiglas cube with down into objects; a carboy with water which is shaken vigorously, so that you can watch the air bubbles during casting.
  • Even when diving or bungee jumping, the body of the jumper feels (even if only for a few seconds ) weightless, until the water surface is touched or tightens the rubber rope. In a jump from a height, for example with the parachute, the feeling of weightlessness ends after a few seconds because the air resistance is clearly noticeable then.
  • Long seconds of weightlessness, you can also enjoy various rides at amusement parks, especially roller coasters and free fall towers. In fan - jargon it is known there airtime.
  • An ancient application of " weightlessness " is the production of buckshot. Here you let liquid lead inside a shot tower rain down through a fine sieve. During the free fall, the lead drops to take the ball round shape.

Experiments in the ( approximate ) zero gravity

  • If a plane flies in a special parabolic trajectory, which is open downward ( the vertex is then above). Such parabolic flights can bring about the feeling of weightlessness up to 90 seconds. Parabolic flights are for research purposes and used in an astronaut / cosmonaut training. There are in different countries commercial parabolic flights.
  • For all spacecraft that orbit in orbit around a celestial body (actually only around its center of gravity). Describing the situation in the accelerated system of the spacecraft, so here is the centrifugal force, the inertial force, which compensates for the gravity.
  • From microgravity one also speaks at Suborbitalflügen during which the effect of gravity, although greatly reduced, but still measurable.
  • Images from the Space Shuttle from a mounted camera show how several astronauts float in the Spacelab and work there. Then, the control nozzles of the shuttles are briefly operated in the transverse direction. The result is that everything that is not bolted - so the astronauts and various loose equipment - parallel to move because of its inertia to each other on a shuttle inside wall until they anprallen there and re-synchronize with the movement.
  • Something quite similar to the weightlessness experienced in a plunge pool. This allows for long periods of time that are used in astronaut training to practice repairs of the spaceship in spacewalks. Such a large exercise pool for cosmonauts located for example in Star City near Moscow. This exercise equipment is also used by ESA and will be trained in assembly of the ISS.
  • The 146 meter high drop tower Bremen makes a total drop of 110 m in an evacuated pipe of 3.5 m diameter. However, in this case, great height, the fall time is still relatively short, it is exactly 4.74 seconds. The experiments are carried out in a specially designed case, the capsule, which is braked at the end of the drop section at an 8 m high, is filled with fine-grained granular polystyrene container. There the " test candidate " a top speed of 167 km / h Since 2004, the tower also has a catapult with which the drop capsule can be shot into the air. Here, the experiment then experiences for about 9.2 seconds of weightlessness, as well as the climb already a " free fall " is.
  • A "mini drop tower " of about two meters allows a fall time of 0.6 seconds, which is sufficient for observation and evaluation by means of video signal and the computer. Students of a Bremen High School studied at "Young Scientist 2002 " in this way physical phenomena such as capillary force, surface tension or combustion processes: Magnets flying apart, water surrounds air and a candle flame looks quite different.

Candle flame in microgravity

Technical problems in weightlessness

Weightlessness can cause problems in sensitive technical devices ( especially those with numerous moving parts ). Physical processes that depend on the action of the weight of bodies (such as convection, see, for example, candles or the water boil), work in a weightless state just as everyday devices such as showers, sinks or toilets. Therefore, in space shuttles and space stations tailored to the specific gravity sanitary facilities (such as a toilet with sewage suction unit ) in use. Is drunk in space not from cups or glasses, but from sealable tubes or cups with lid and lockable straw.

But Weightlessness also offers many technical advantages over the possibilities that we have on earth. So can be better observed, for example, the adhesion force and the properties of surface tension, which is not least a big step forward for the study of the microcosm. An example of an observation that one can make in everyday life to free-falling liquids, is the chain-like deformation of a column of water (fountain, small waterfall ), which occurs when the surface tension tries to form spherical droplets, while the cohesion tried the water column together. For space stations weightlessness offers the advantage of optimum space utilization, as can also be mounted on walls and on the ceiling equipment.

Reaction of the human body to gravity

The human body reacts to the feeling of weightlessness often with space sickness, which is just like the motion sickness caused by a disorder of balance.

With progressive habituation to the weightless state, the characteristic of the space sickness symptoms disappear (dizziness and nausea to vomiting). Prolonged weightlessness (2 months or more) leads to an adaptation of the human body to the ( noticeable especially in the spine and leg area ) Discharge: bone and muscle mass as well as the volume of blood fade what many astronauts upon return to Earth health problems prepares. For prevention must spaceman on long-term use therefore ( on a treadmill or ergometer) by exercise of weightlessness oppose an artificially generated resistance. 2012 showed studies on astronauts also changes in the brain and eyes.