A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

If everyone in China jumped off chairs at once, would the earth be thrown out of its orbit?

April 6, 1984

Dear Cecil:

I hope you can answer a question that has plagued me since childhood. If every man, woman, and child in China each stood on a chair, and everyone jumped off their chair at exactly the same time, would the earth be thrown off its axis? Also, if prior to jumping, they all yelled at the top of their lungs, would we hear it here in the United States, and how much of a time delay would there be?

Cecil replies:

Believe it or not, I'm actually going to answer this ridiculous question. But first we need to have a word.

As you can imagine, I possess phenomenal scholarly resources. I've converted the spare bedroom in my house into a research library containing 16 million volumes, which are dusted twice a day by a team of robed acolytes holding candles. I have instant access via my Apple 380S GT to all the world's data banks. Why, right here on my writing table next to the box of spare quills I have a dog-eared copy of 16,000 Unbelievably Complicated Physics Experiments for the Home and Garden, With Answers, which has helped me out of many a jam.

Despite this wealth of scientific knowledge, the Teeming Millions routinely write in with questions that, in 6,000 years of recorded history, no one has ever asked. As a result, my usual sources of information are useless.

Nonetheless, I try. I've been in contact all week with the Beijing government in an effort to persuade them to get all 1,027,000,000 Chinese (1980 estimate) to jump off chairs. I've pleaded with them that will signficantly advance the cause of science. However, they refuse to cooperate.

They point out that China is a poor country, and lacks sufficient chairs. Moreover, many of the chairs that are available are of nonuniform height, meaning that even if all the Chinese jumped off at the same time, they'd hit the ground at different times, throwing off the results.

Finally, they point out that discipline among the Chinese people has become lax since the Cultural Revolution, and that many of the participants in the project would likely be distracted when they were supposed to be jumping. The Chinese government suggests that instead of having the entire nation jump off chairs, I should get one representative citizen to jump and multiply the results by 1,027,000,000. I have, needless to say, rejected this solution as grossly inadequate.

The possibility of an actual test thus being remote, I've been forced to work this out on the basis of reason alone, to wit: given that every action has an equal and opposite reaction, when the Chinese get up on their chairs, they'd 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, 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 in orbit.

Just for fun, however — after you've been doing this job for a while you get a pretty unusual notion of what constitutes a good time — 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 feats of mathematics requiring the entire afternoon — 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. What would happen if all the Chinese yelled at the top of their lungs I refuse to even discuss.

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