Everything in the universe that has mass, has gravity.  It’s easy to understand that the Earth, large as it is, has gravity, which pulls on us constantly, keeping us on terra firma.  It’s just as easy to understand that other large objects have gravity, like the Moon, planets, and the Sun. However, it’s much harder to understand that every person on Earth has gravity.  Strangely, you exert a force on the Earth, and on every other human.  You also exert a force on every rock, tree, and creature that roams the Earth, and they all exert a force on you....