# Can You Describe Weightlessness In Satellites And Gravity Free System?

Weightlessness in Orbit

Earth-orbiting astronauts are weightless for the same reasons that riders of a free-falling amusement park ride or a free-falling elevator are weightless. They are weightless because there is no external contact force pushing or pulling upon their body. In each case, gravity is the only force acting upon their body. Being an action-at-a-distance force, it cannot be felt and therefore would not provide any sensation of their weight. But for certain, the orbiting astronauts weigh something; that is, there is a force of gravity acting upon their body. In fact, if it were not for the force of gravity, the astronauts would not be orbiting in circular motion. It is the force of gravity which supplies the centripetal force requirement to allow the inward acceleration which is characteristic of circular motion. The force of gravity is the only force acting upon their body. The astronauts are in free-fall. Like the falling amusement park rider and the falling elevator rider, the astronauts and their surroundings are falling towards the Earth under the sole influence of gravity. The astronauts and all their surroundings - the space station with its contents - are falling towards the Earth without colliding into it. Their tangential velocity allows them to remain in orbital motion while the force of gravity pulls them inward.

Many students believe that orbiting astronauts are weightless because they do not experience a force of gravity. So to presume that the absence of gravity is the cause of the weightlessness experienced by orbiting astronauts would be in violation of circular motion principles. If a person believes that the absence of gravity is the cause of their weightlessness, then that person is hard-pressed to come up with a reason for why the astronauts are orbiting in the first place. The fact is that there must be a force of gravity in order for there to be an orbit.

One might respond to this discussion by adhering to a second misconception: The astronauts are weightless because the force of gravity is reduced in space. The reasoning goes as follows: "with less gravity, there would be less weight and thus they would feel less than their normal weight." While this is partly true, it does not explain their sense of weightlessness. The force of gravity acting upon an astronaut on the space station is certainly less than on Earth's surface. But how much less? Is it small enough to account for a significant reduction in weight? Absolutely not! If the space station orbits at an altitude of approximately 400 km above the Earth's surface, then the value of g at that location will be reduced from 9.8 m/s/s (at Earth's surface) to approximately 8.7 m/s/s. This would cause an astronaut weighing 1000 N at Earth's surface to be reduced in weight to approximately 890 N when in orbit. While this is certainly a reduction in weight, it does not account for the absolutely weightless sensations which astronauts experience. Their absolutely weightless sensations are the result of having "the floor pulled out from under them" (so to speak) as they are free-falling towards the Earth.

Still other physics students believe that weightlessness is due to the absence of air in space. Their misconception lies in the idea that there is no force of gravity when their is no air. According to them, gravity does not exist in a vacuum. But this is not the case. Gravity is a force which acts between the Earth's mass and the mass of other objects which surround it. The force of gravity can act across large distances and its affect can even penetrate across and into the vacuum of outer space. Perhaps students who own this misconception are confusing the force of gravity with air pressure. Air pressure is the result of surrounding air particles pressing upon the surface of an object in equal amounts from all directions. The force of gravity is not affected by air pressure. While air pressure reduces to zero in a location void of air (such as space), the force of gravity does not become 0 N. Indeed the presence of a vacuum results in the absence of air resistance; but this would not account for the weightless sensations. Astronauts merely feel weightless because there is no external contact force pushing or pulling upon their body. They are in a state of free fall.
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When satellite is falling freely in space, everything within this freely falling system will appeare as weightless and this condition is known as weightlessness.

As the space ship is accelerating towards the centre of Earth at all times since it circles round the Earth.  Thus no force is required to hold this space ship.  "A system in which no force is required to hold an freely falling object is called "gravity free system"

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When a satellite is falling freely in space, every thing within this freely falling system will appear to be weightless. It does not matter where the object is, whether it is falling under the force of attraction of the earth, the sun, or some distant star.

As a earth's satellite is a freely falling object, the statement may be surprising at first, but it is easily seen to be correct,considering the behaviour of a projectile shot parallel to the horizontal surface of the earth in the absence of air friction. If the projectile is thrown at successively larger speeds, then during its free fall to the earth, the curvature of the path decreases with increasing horizontal speeds. If the object is thrown fast enough parallel to the earth, the curvature of its path will match the curvature of the earth.

The space ship is accelerating towards the center of the earth at all times since it circles round the Earth. Its radial acceleration is simply g, the free fall acceleration. In fact, the space ship is falling towards the center of the earth, because of spherical shape of the earth; it never reaches the surface of the earth. Since the space ship is in free fall, all the objects within it appear to be weightless. Thus no force is required to hold an object falling in the frame of reference of the space craft or satellite. Such a system is called gravity free system.
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http://www.physicsclassroom.com/class/circles/Lesson-4/Weightlessness-in-Orbit

Weightlessness in Orbit

Earth-orbiting astronauts are weightless for the same reasons that riders of a free-falling amusement park ride or a free-falling elevator are weightless. They are weightless because there is no external contact force pushing or pulling upon their body. In each case, gravity is the only force acting upon their body. Being an action-at-a-distance force, it cannot be felt and therefore would not provide any sensation of their weight. But for certain, the orbiting astronauts weigh something; that is, there is a force of gravity acting upon their body. In fact, if it were not for the force of gravity, the astronauts would not be orbiting in circular motion. It is the force of gravity that supplies the centripetal force requirement to allow the inward acceleration that is characteristic of circular motion. The force of gravity is the only force acting upon their body. The astronauts are in free-fall. Like the falling amusement park rider and the falling elevator rider, the astronauts and their surroundings are falling towards the Earth under the sole influence of gravity. The astronauts and all their surroundings - the space station with its contents - are falling towards the Earth without colliding into it. Their tangential velocity allows them to remain in orbital motion while the force of gravity pulls them inward.

thanked the writer.