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# How does gravity work?

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To the extent that scientists understand gravity, it is a product of geometry; gravity is a curvature in the space-time continuum, and the extent of the curvature is determined by the extent of an object's mass. The curvature around Earth makes the moon stay nearby, and the curvature around the sun causes the planets of our solar system to orbit it.

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An analogy often used to help people understand gravity is this: place a large marble on a rubber sheet and observe how the sheet indents; the marble represents the sun and the indentation represents its gravitational pull. Place a smaller marble representing Earth on the sheet and observe how the indentation of the rubber sheet causes the smaller marble to roll toward the larger.

As of 2015, though, science's understanding of gravity has not yet been reconciled with its understanding of particle physics. Dividing the two topics is a threshold called the Planck length, which is extraordinarily small. Anything smaller than the Planck length is best understood through a theory known as quantum mechanics, while anything larger is best understood using Albert Einstein's theory of relativity. Until science has a unified field theory reconciling relativity and quantum mechanics, science cannot honestly claim a full understanding of gravity.

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## Related Questions

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The force of gravity between two objects is determined by the mass of each object and the distance between their centers. Objects with a greater amount of mass will exert a greater degree of gravitational pull, but as the distance between two objects increases, the gravitational force between them lessens. The significance of distance with regard to large masses, such as planets, plays an important role in the science of Astronomy.

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Weight is a measurement of the force placed on an object by gravity, whereas mass is the amount of matter an object contains. Mass is commonly denoted using m or M, and weight is denoted with W.

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There are two formulas that may be used to calculate mass: mass is equal to the volume of an object multiplied by its density (m=v*d) and mass is equivalent to an object's weight divided by the acceleration of gravity (m=w/g). The appropriate formula depends on the available variables.

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There is no air in space because there is no gravity to condense the molecules of gases found there into air. On Earth, gravity holds nitrogen, oxygen and the other gases that compose the atmosphere together, but only to about 60 miles above the surface.