Sunday, 27 February 2005

World Jump Day

You too can stop global warming! Just jump at the right time. Of course, I don't know how to judge the physics - fact or farrago? In any case it only caters to those in timezones from the International Date Line to +2 GMT (Istanbul), so those of us in the opposite part of the world will just brace ourselves for the impact.

Edit: welcome to all my Belgian visitors! Any chance of sending over mussels and beer?

This is a joke right? A little physics should convince you how incredibly stupid this is.

1. For a person to jump off the surface of the Earth, Newton's Third Law guarantees that the Earth will feel a reaction force equal and opposite to the force generated by jumping. This then to an excellent approximation cancels the impulse of the force generated on impact. The only effect of 6 billion jumping human beings will be lots of sore kneecaps and a few stress lines in concrete all over the world, and the earth's days changing ever so slightly in duration.

2. Imagine for a moment that Newton's Third Law is suspended. Then if the average person weighs 60 kg and manages to attain an impact velocity of 10 m/s in one jump, the collective momentum imparted by 6 billion jumping human beings is 3.6x10^12 J.s. This is enough momentum to change the velocity of the earth (with a mass of 6.0x10^24 kg) a grand total of 6x10^-11 m/s. Considering the orbital velocity of the earth is 30 km/s, this change is as good as nothing.

3. Celestial mechanics guarantees that if escape velocity is not attained, the earth will only be perturbed about its current orbit. The average distance from the earth to the sun will not change; instead the proposed actions (multiplied ten-quadrillion fold, i.e getting everyone to jump once a day at the right time for 27 billion years) will only succeed in wobbling the earth's orbit, the least of which would result in climatic chaos. The animation on the website is completely bogus.

4. The only possible effect on the earth would be changing its angular momentum. Assuming the average human stays aloft for two seconds during the jump, the angular change of the earth due to rotation is 0.5'. So the maximum possible change in angular momentum due to World Jump Day is 1.3x10^8 J.s, which is enough to change the earth's angular momentum about its axis (which is 1.8x10^34 J.s) by a factor of 7x10^-27, which would reduce the length of the day by 6 x 10^-21 s.

Geez, and professional scientists wonder why the public continues to be ignorant of science.

Some of my friends are the size of Fat Albert and Yokozuna. I'll ask them to jump with me.

Haha. I guess it's all done for a bit of fun.

Yeah, acid, just wanted a chance to use the phrase "fact or farrago" in a post. :) But thanks for the detailed explanation!

I know it violates the laws of physics, but you see, I never studied law. [/bugsbunny]

i am not sure that 'farrago' (which i understand to be synonymous to 'hodgepodge') is quite the antithesis to fact that you are looking for. i do think that 'hodgepodge of facts' is a semantically valid construction.

i hope your bugs bunny imitation doesn't include nibbling on raw carrots; as far as i can tell, they don't make one any wheatier. ;)

Why jump all at the same time?Jump at local time.I mean The world is devided in timezones,so every timezone jumps with one hour difference but at the same it?So there is no one jumping at the opposite and all force off jumping puches in the same direction.The idea is good but i don't know about the effect.

Only mussels and beer ? No chocolate and waffles ?? ;-)

Hey, I'm not a demanding person. Good mussels and beer will do, although some pralines and other chocs would of course be welcome.

And... any idea what earthquake that would give? I bet China and India would be completely off the maps if everyone there jumped at the same instant...

obviously this isnt goin to work but did you know that if it did the temperatures obtained would melt the ice caps, flooding the coasts, utterly destroy the earths ability to make nitrogen or somethin like that and kill all the plants in a little while.
This would make the co2 levels skyrocket, and i'm not sure what would happen first.
If we would suffocate from lack of oxygen, starve from lack of food, or incinerate from huge temps

hola felicitaciones que buena idea suerte

La idea es tan idiota que no creo que ni valga la pena que hable sobre ella. No les enseñan un poco de física o de pensamiento lógico en la escuala. Espero que no haya sido más que una broma, pues lamentaría que las personas de nuestro planeta se estén volviendo tan idiotas. ¿Y si en vez de saltar soplan todos para arriba? :D

wtr acidflask's comments -

You've made some interesting calculations, and I'm not going to try and argue that the collective force of a billion people jumping is going to have the slightest influence on the Earth's orbit- of course it won't. From a physics point of view, though, I have to question a couple of your assumptions - most notably that the influence on the Earth of pushing off and landing would not cancel each other out - in fact they reinforce each other. Both are downward impulses on the Earth's surface, so both influence it in the same direction.

In terms of celestial mechanics, while it's certainly true that orbits are a fairly stable equilibrium (and hence slight deviations tend to be self-correcting), they can be adjusted and still remain stable in their new configuration, even without acheiving escape velocity. The orbit represents a balance of forces between gravitational attraction (towards the centre of the orbit) and angular acceleration (at a tangent to the orbit). The gravitational force is related to the distance between the bodies, and the angular acceleration is related to the speed at which the orbiting body moves along the orbit path. Therefore it is theoretically possible to increase the distance from the gravitational centre and still have a stable orbit, provided that the speed of the orbiting body is reduced.

if you look on there the calculator would make everyone jump at the same time, which means everyone would cancel each other out

Thanks Mikespoff - I love the physics discussions going on.

Oh, and to the previous commenter, I think only half the world is supposed to jump at one time...

LOL,who had this stupid idea?
Why dont we all blow upwards at the same time? It should change the Earth's orbit as well
Newton's third law says that for every action or force there is an equal and opposite reaction.
So if we all blow upwards at a certain point on the planet, the Earth showld move in the opposite direction.
May be we could all fart at the same time; but tell the indians and the chinesse to join, otherwise It's not gonna work. (we should eat lots of baked beans if we were gonna try this method)

I don't think that a few million people jumping (and yeah it will be only a few million) will have any effect on the Earth...I mean come on...does the Earth change orbit when buildings fall down (New York), when bombs are dropped, when volcanoes erupt, or when I drop a massive deuce? No, and these events will all be much more powerful than some people hitting the ground...blah

We have to live by the 95% rule. Which means that 95% of the people on this early don't know what the hell they are talking about.

I don't think that anyone one should jump if it alters earths weather in any way you would be messing with mother nature so DO NOT JUMPand please tell all your friend's NOT TO JUMP

Ah yes we have the person who believes we should not alter Mother Nature. I believe driving a car which has emissions and using electricity which has to come from somewhere. So my answer to you my friend is unless you plan on never driving again or using electricity in any form ( which includes any products made with the use of electricity or shipping which is basically everything) then you cannot tell people to not mess with mother nature unless you are a hypocrite.

Simply put... this idea violates both the conservation of energy and angular momentum... no question. These are the two factors that determine the size and eccentricity of an orbit.

As stated in the Newton's 3rd law "to every action there is an equal and opposite reaction",htis phenomenon implies at this point...
So if a large mass of people jump at the same time it will create some kind of force so in turn which will give rise to a reaction.
So it is possible that the reaction can be in the way that the orbit can the earth is a bit inclined....

So let me get this straight... we could then theoretically keep doing it and get the earth moving farther and farther away and each time faster and faster. Now for some reason it would seem with nothing leaving the earth how could it propel itself farther and farther away while increasing speed? Seems that for something to go forward the same force is moving in the opposite direction aka towards the sun but we do not have that here.

The center of mass of earth motion is governed by the resultant of external forces (gravitational, magnetic...etc. etc.): R = M*a.
If there is no external force the center of mass of earth moves with constant speed in a stright line: in this case no internal force (like those from the jump)can change the motion of the centre of mass.
But this is not the case : here we are in presence of external forces.
My doubt is : can internal forces (and mass distribution variation) cause a change in external forces ? If yes the orbit could be changed in principle. Surely the rotation period of the earth can be changed by redistribution of mass !


Indeed it can. If we pack up all the mass of the earth in a smaller sphere, the earth will rotate faster. Basically because the parts of it which are farther from the centre need to rotate faster than those closer to it; hence, if we put the superficial mass closer to the centre, the earth will have to spin faster. But as to putting the earth into a lower orbit or making years shorter, only the earth and sun masses are involved, no concern for their shape at all.

i like eggs

yes, this sure seems to have the aroma of a big stinky hoax and will surely get much media coverage nearer the time. all the while they are making a tidy sum selling their t's and window stickers. hey, you got to hand it to them for trying.

It´s funny how people who acclaim to have knowledge in phisics are the people that heard about the laws but have no idea about how to apply it.
1. Newton´s third law is not correctly mentioned here, because there are two different events: on the 1st moment you jump, and you apply a force on earth´s surface. On the second moment, you fall down and apply a second force on earths surface. Any force is cancelled here.
2. The speed generated by the impact, calculated by our friend as being 6x10^-11 m/s, is orthogonal to the speed of rotation (30 km/s), and so has no influence to it.
3. It´s right that the average distance from the sun will not change, but the trajectory will.
4. About angular momentum, will there be a change since the average ratio of the orbit will be higher, and the shape of earth will not change?
I agree that most of people are ignorant of science, but I would like to see here if someone can explain why wjd can not work.
I will give the right answer on july 19th.

Well I don;t know whether to believe it or not but I do question whether this will have an effect on the tectonic plates. Wouldn't that sudden pressure (being the plate(s) are pushed downward) have an impact on all volcanic activity in the area? What if this causes all the volcanos in the western hemisphere to all go off at once? I'm not claiming to have an data on this, im just lloking at it from all angles and hoping someone else tells me im wrong and the world isnt ending on july 6th.

Don't forget that they want to increase daylight hours, WHILE cooling it down. Even if it did work, it still would cancel itself.

Anyone who thinks this will work is a complete retard.

From what I can tell from acidflask's calculations, and some of my own and others, the effect this will have would be the same as putting on SPF 1.0000000000000000000025 sunscreen...

I think I'll just stick to SPF 45+ please :p

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