Weightlessness (or zero-g) is any condition equivalent to experiencing little or no acceleration or gravitational attraction, e.g., far from a planet, star, or other massive body. From the equivalence principle for acceleration and gravitational attraction it follows that weightlessness can also be experienced in free fall, which is the cause of weightlessness of objects in orbit about the Earth. The orbit is maintained by the object's inertia tangential to its flight path and its acceleration towards the center of the Earth,[citation needed] resulting in a curved orbit around the planet. An astronaut inside an orbiting vehicle has the experience of floating because the person has the same acceleration as the capsule.
The human body is adapted to the gravitational field at the surface of the Earth and a weightless environment can have adverse effects on human health.[citation needed] In the short term, these may include space sickness, while in the long term more serious problems such as muscle atrophy and bone loss may develop.
Weightlessness can be realised for short periods of time in an airplane following a specific parabolic flight path, or (as a simulation with many differences) in neutral buoyancy in a tank of water.
The term zero gravity literally only refers to the complete absence of gravity, something which essentially cannot happen within the solar system due to the Sun's gravity, but is usually used synonymously to mean weightlessness. Microgravity (or µg) is used to refer to situations that are substantially weightless but where the g-force is around a millionth of that at the Earth's surface.
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The human body is adapted to the gravitational field at the surface of the Earth and a weightless environment can have adverse effects on human health.[citation needed] In the short term, these may include space sickness, while in the long term more serious problems such as muscle atrophy and bone loss may develop.
Weightlessness can be realised for short periods of time in an airplane following a specific parabolic flight path, or (as a simulation with many differences) in neutral buoyancy in a tank of water.
The term zero gravity literally only refers to the complete absence of gravity, something which essentially cannot happen within the solar system due to the Sun's gravity, but is usually used synonymously to mean weightlessness. Microgravity (or µg) is used to refer to situations that are substantially weightless but where the g-force is around a millionth of that at the Earth's surface.
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