If all Chinese jumped at once, would cataclysm result?

Cecil's Columns/Staff Reports
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If all Chinese jumped at once, would cataclysm result?:
"The possibility of an actual test thus being remote, I have been forced to rely on my considerable powers of inductive logic, to wit: given the principle that every reaction 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.
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The last bit there… i’ve just started learning about newton’s laws… but doesnt the third law (the one of action and reaction) state that the opposing forces do NOT “cancel each other out” ?

@_@

I have edited in a link to the column under discussion. – CKDH

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Cecil’s use of “action and reaction” canceling each other out got entangled with his use of Newton’s third law “action and reaction”. They were not interchageable. The Newton’s Third law set of action and reaction refers to the fact that a force acts in both directions, or is felt on both halves. Or forces happen in pairs. Say you push on a door. If the push is light and the door resistance heavy, the door does not move, and the door pushes back on your hand equivalently. If the push is harder and/or the door lighter, some of the push is absorbed by the movement of the door, and some is the push back on your hand.

The other set, the one Cecil uses, is the action of getting up on the chairs and the reaction of falling back to the ground. This is not a third law pairing, but a potential energy demonstration. Cecil does word this poorly.

Or you can interpret it differently. The action of climbing up on the chairs has the reaction of pushing the Earth slightly away from where it was. Then the action of stepping off the chairs has the reaction of the Earth shifting back to where it was as the Chinese people fall to the Earth. Thus the action and reaction are not canceling out, but the actions are canceling each other out.

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I’m dumb at physics, so forgive me if this is a stupid question, but…

What if all the Chinese people put FORCE into their jump? If they exert some of their own energy (from food or conversion of fat to energy or whatever)? Wouldn’t that energy be greater than the energy needed to lift the mass of the fat molecules or whatever onto the chair, and so therefore contribute more energy to hitting the Earth? Or would that be counterbalanced by the energy needed to push off the chair in the first place. I mean, if I just step off something, I can hit the ground kind of lightly, but I might also be able to “kick” in mid air and apply more force…do you follow what I’m wondering about?

I doubt it would still have a noticeable effect on the Earth, but what about on a smaller scale (at least theoretically?)

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Explain how a kick in the air can make you have more downward force.

If you kick in mid air, there is nothing you can do to make yourself go down any faster. (Well, there is the issue of air resistance and drag, but that is completely irrelevant at the height of a chair.) You may be expending your internal energy to move your parts around relative to each other, but you are not doing anything to give yourself a downward push, because you are not pushing against anything.

So you push against something as you jump down. What do you push against? If it is fastened to the ground (bolts, nails, cement, welded, etc), then the energy you are putting into the push is going into the ground, and you are pushing the ground up in order to push yourself down, ergo canceling out that extra push. You may hit the ground a little quicker, but the net effect on the Earth/person system is zero. If the object you push against is not fastened, then you are just pushing that object up against the field of gravity, at which point it will then return to a neutral state (i.e. fall back to the ground). Ergo, no net change to the overall system. The Earth went nowhere.

Think of it this way - if you are able to affect something in order to make yourself fall faster, then that object has to deal with the effect. You cannot make yourself fall faster without affecting some other object.

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The simplest way to look at this, is that they can’t move the center of mass of the Earth-people system. The only way to accelerate the center of mass of a system is to have a force from outside the system (this is another way of expressing Newton’s third law). Since we have only forces internal to the system, we can’t do anything to the center of mass.

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If anyone’s interested my high school phsyics teacher had a tabloid cover on his wall with a story about the Communists planning for all the Chinese to jump at the same time and throw the Earth out of orbit. Whether this idea came from the article or not I dunno. But maybe that’s the origin.

The article also talked about organizing Americans for a counter-jump. I think it might have also had a picture of a big boned person, who would be able to counteract the effect of several smaller Chinese people. Either that or my friend and I made that part up as a joke.

As for a scientific explanation, I’ll try my hand. Let’s see if I remember my physics. So there are 1.5 billion Chinese. Let’s say they each have a mass of 68 kg (weight of about 150 lbs). Let’s just say that mass of (1,500,000,000 * 68) = 102,000,000,000 kg hits the earth at a speed of 9.8 meters per second. (That’s about how fast something would be going after a second of falling, ignoring air resistance). So the momentum (momentum = mass times velocity) of this falling group of Chinese is 102,000,000,000 * 9.8 is about 1,000,000,000,000. In scientific notation that’s 10^12 (kg*m/s). By conservation of momentum we can say that the Earth will gain the momentum of the impacting group of Chinese. The change of Earth’s momentum equals Earth’s mass times its change in velocity because of the Chinese. We know the imparted momentum (10^12) and we know Earth’s mass (about 10^24 kg). So we can calculate the velocity change. So Earth’s velocity is the imparted momentum divided by its mass. This is: 10^12 divided by 10^24 which is a whopping 10^-12 or 0.000000000001. So the Earth would have gained a veolcity of 0.000000000001 meters per second, which is basically zero. So nothing would happen.

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One thing to add. This is assuming the jumping Chinese started as an entity independent of the Earth. Not a valid assumption, but one that only increases the likelihood for them to do something. So my situation is more like if a UFO from outer space lifted up all the Chinese and then dropped them.

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I’m no expert, but I suspect their distribution would have something to do with it, too. I mean, we’re talking a billion screaming Chinese, averaging roughly a hundred pounds each, assuming we include ALL of them, diapers to cane, right? So, for convenience’s sake, we have a hundred billion pounds here. I strongly suspect that if we scattered it all over China in convenient hundred-pound packages, we wouldn’t see a whole lot of tectonic plate activity the next day.

If, on the other hand, the aliens dropped them all in Beijing, well, that’s another matter.

Altitude counts, too. Plainly, you’re not going to achieve terminal velocity in the time it takes you to leave the chair and strike the floor. There’s a very limited amount of energy built up in that leap, kids.

If, on the other hand, the aliens dropped them from, say, a couple hundred feet up, well, this is another matter. Even then, though, due to the essentially liquid nature of human biomass (as compared to the considerably more solid nature of most things these Chinese would be landing on), much of the impact would be wasted sideways, as these poor Chinese basically splattered all over the landscape.

I must, therefore, without actually breaking out the calculator, assume little or no catastrophe, at least in a geologic or seismic sense.

The results of a billion screaming Chinese tumbling out of the skies all over hell and gone, on the other hand, may be considered catastrophic in the extreme…

…so my actual response must be: “Could you rephrase the question, please?”

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That depends on whether the relevant quantity here is energy or momentum. If we’re trying to change the Earth’s orbit, we’re interested in momentum, and momentum cannot be “wasted sideways”. If, on the other hand, we’re interested in earthquakes, then energy might conceivably be the relevant quantity (paging RM Mentok!).

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Oh. Sorry. I was thinking “generic cataclysm” as opposed to a specific one, like hurling the Earth into the sun or something…

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A few billion Chinese, a billion five-hundred million pounds.

We have seen (or experienced) the Earth hit by objects of unknown mass at greater velocity (the Tunguska blast) without the Earth’s orbit affected, and have set off nuclear test devices (bombs) over and over, many of which had the force of millions of tons of TNT being exploded, with no measurable effect on the Earth’s orbit, rotation, etc.

I think the power of any of the above would exceed even the whole world’s population jumping off chairs in China.

Breathe easy, that’s not how it’s gonna happen.

(But, if they DID do that… would we be knocked off our chairs in Kansas?) :dubious:

Ed is on no side.

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No, no effect in Kansas.