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Gravity is the change in the geometry of spacetime generated by a massive object sitting in spacetime. However, in terms of everyday experience, gravity is the force which a massive object generates that attracts other objects to it...e.g. the gravity of the Sun helps keep the Earth in orbit about itself. Or, makes an apple fall to the ground when an apple breaks off an apple tree.
Daniel....gravity is a natural phenomenon as well as a "force" and is one of the fundamental "forces" of nature (like EM, WN and SN). It's the weakest of all the "forces"...some 10^39 times weaker than EM. Yet its influence is universal and overwhelming. What we don't know about gravity is what it actually is... we call the particle that supposedly carries the gravitational "force" a graviton. However we have never detected gravitons....they're hypothetical. We also don't know why it's so weak. We have ideas as to why it is, but they remain speculation. In actual fact, we know very little about gravity and what it is, other than what we can observe.
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