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given the principle that every action has an equal and opposite reaction, when the Chinese get up on their chairs, they would essentially be pushing the earth down in the process of elevating themselves. Then, when they jumped off, the earth would simultaneously spring back, attracted by the gravitational mass of one billion airborne Chinese persons, with the result that the Chinese and the earth would meet somewhere in the middle, if you follow me. The upshot of this is that action and reaction would cancel each other out and the earth would remain securely in orbit.

Just for fun, suppose 1,000,000,000 Chinese, give or take 27,000,000, were somehow to materialize atop chairs without their having to elevate themselves thereto. And suppose they jumped off.

Having performed astonishing feats of mathematical acrobatics (requiring the entire afternoon, I might note--sometimes I can't believe the crap I spend my time on), I calculate that the resultant thud in aggregate would be the equivalent of 500 tons of TNT Not bad, but nowhere near enough to dislocate the earth, which weighs 6 sextillion, 588 quintillion short tons

The earth tremor that generated the Tsunami not only slowed down the rotation of the earth for a moment but also considerably changed the pace and sequence of events in the Sri Lankan political arena as well.

NASA Details Earthquake Effects on the Earth
NASA scientists using data from the Indonesian earthquake calculated it affected Earth's rotation, decreased the length of day, slightly changed the planet's shape, and shifted the North Pole by centimeters. The earthquake that created the huge Tsunami also changed the Earth's rotation.