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# What Causes Weightlessness in Space?

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Weightlessness is a theoretical state where a body exists uninfluenced by any gravitational forces. In fact, even at great distances, large astronomical bodies such as planets and stars continue to exert gravitational influence, but if the distance is great enough, that influence becomes negligible. The directions of up and down are defined by the pull of gravity. With no up or down, a body floats.

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Every object with mass exerts a gravitational influence. The magnitude of this influence increases with the mass of the object and decreases with the distance between the objects in question. A planet has a huge mass and therefore exerts a huge gravitational influence. Reaching the point where the influence of Earth's gravity is negligible requires travelling a great distance. At a distance of 125,000 miles from Earth, or more than halfway to the Moon, the influence of Earth's gravity is about one thousandth what it is on the Earth's surface. In Earth orbit, the effect of Earth's gravity is only slightly reduced, but people in orbiting spacecrafts feel weightless because of the immense speed at which they are travelling. The force of gravity keeps the ship from flying off into space, and the force caused by the velocity of the ship keeps the ship in orbit. In essence, a ship in orbit is falling around the earth. In orbit, everything is being pulled towards the Earth at the same speed, giving objects the appearance of floating. The same effect is achieved in a free-falling aircraft.

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