Can a Large Group of People Really Change the Earth's Rotation?

[Pengwuino]

http://www.worldjumpday.org/

what really gets me is how they actually have almost 200 million people registered

 

[brewnog]

Fantastic!

This reminds me of the one where they tried to get everyone to shine their laser pointer at the moon at the same time in order to put a red spot on it!

 

[Jimmy Snyder]

what really gets me is how they actually have almost 200 million people registered

What gets me is that you believe them.

 

[Pengwuino]

Oh i don't believe them. I just think there insane.

unless your tlaken about the # of registered users... which yah, that does seem way off base for a site I've never even heard of...

 

[darkar]

Dont think it will really works... But haha, sit down, hold popcorns and watch their actions.:P

 

[Pengwuino]

lol, be funny if they start a huge series of earthquake and just kills half hte worlds population...

 

[BobG]

I think it's a capitalist American plot (only people in the Western hemisphere are supposed to jump). Never fear - the Chinese are on to them and are planning a counter jump at precisely the same instant. I anticipate no net effect.

Then again, there may be a super secret plot behind the exposed plot. The only way there would be a net effect is for the 600,000,000 to jump off the face of the Earth and into their own orbit around the Sun. The real net effect of the original jump and the counter jump will be to rid the Earth of 1.2 billion people, thereby pushing the disasterous effects of overpopulation (currently 6 billion) a few decades into the future. Pretty ingenious when you think about it.

 

[Pengwuino]

You really know how to find out the truth to these matters don't you Bob

 

[darkar]

BoB, could u actually the one behind the plot?

 

[Pengwuino]

He obviuosly is. I mean look at his avatar...

 

[mapper]

If everyone in the Earth's northern hemi jumped would people in Australia fall off the globe?

Ive signed up on the this site a year or two ago. Forgot about it.

 

[JamesU]

I signed up for the hell of it. I still haven't dacided whether to jump or not. but these people are the stupidest people I've ever heard of. they think that 800,000 people will jump and move the earth? I just would like to see it fail so all their members cab laugh in their face

 

[Moonbear]

This one's been circulating for a while. Would anyone care to apply their physics knowledge to show why it won't work?

 

[yourdadonapogostick]

well, it would make a force when they jump, but another in the opposite direction when they land.

 

[Pengwuino]

Well according to E=mc^2 and F=ma, when you use the SinCos trig switch, you determine these people are idiots, thast why it won't work

And wouldn't people just be canceling each other out if one person in china jumps and someone in the US jumps?

 

[Moonbear]

Well according to E=mc^2 and F=ma, when you use the SinCos trig switch, you determine these people are idiots, thast why it won't work

 

[Jimmy Snyder]

This one's been circulating for a while. Would anyone care to apply their physics knowledge to show why it won't work?

My understanding is that it would work in a limited sense. When an individual person jumps up, they gain momentum in a particular direction and the Earth gains momentum in the opposite direction. During the time that the person is in the air, their momentum is constantly changing and so therefor must that of the Earth. I think there should be a ripple in the orbit of the Earth. However, this ripple must escape detection by even the most subtle of measuring instruments. Moreover, I believe the effect on the Earth's orbit is limited to this ripple. After the jump, the Earth would be left in the same orbit it was in before as if the ripple had never occured.

If 600,000,000 people were doing the same thing at the same time and in the same place, it would have a proportional effect. However, there seems to be no effort to bring these people to the same place and so some of the momentum will cancel. I have no idea whether the effect would be measureable. I vaguely remember reading that the earthquake that caused the tsunamis in Asia did have an effect on the orbit of the earth, but I could be wrong. I think the force exerted by 600,000,000 people jumping is miniscule compared to such an earthquake.

 

[brewnog]

The science thread:

https://www.physicsforums.com/showthread.php?t=81503

 

[BobG]

This one's been circulating for a while. Would anyone care to apply their physics knowledge to show why it won't work?

Theoretically, it could work (in a vacuum, at least), provided the jumpers didn't jump perpendicular to the Earth-Sun radius. While the jumper's are airborne, they would be either closer to the Sun than the Earth or further away from the Sun than the Earth. The gravitational attraction of the Sun is inversely proportional to the square of the distance of the orbiting object, so there would be a gravity gradient difference between the jumpers and the Earth. That means that the interaction between the Earth and the jumpers won't quite cancel out perfectly. The orbit of the Earth would be affected. Being in a separate orbit than the Earth, the jumpers wouldn't come down quite straight down relative to the Earth, either. The slight deflection in their downward path would change the rate of rotation in the Earth. Overall, angular momentum would be conserved, but the angular momentum of the Earth's orbit and the angular momentum of the Earth's rotation would each be changed.

In practice, if the average mass of the jumpers were 100 kg, their total mass would 6 x 10^10 kg. The Earth has a mass of 6 x 10^24 kg. It's going to be pretty hard for the jumpers to have much affect on something that's 100 trillion times bigger than them. The difference in the gravity gradient would be pretty small, as well. The distance between the Earth and Sun is about 150 billion meters and the jumpers would be lucky to clear 1 meter.

Perturbations from the other planets in the solar system have much more affect than 600,000,000 jumpers would. In fact, because of other celestial objects besides the Sun, the Earth's orbit and rotation rate are constantly changing and the exact rate of change can't be calculated incredibly accurately (leap seconds used to be manually added into atomic clocks to account for this).

In other words, having 600,000,000 people jump at the same time would be less detectable than a whisper at a rock concert. Still, getting 600,000,000 million people to do the same thing at the same time would be pretty impressive, even if the results were trivial.

 

[shmoe]

I was sure they tried this with school kids somewhere, not to change orbit but cause some tremors. Sure enough:

http://www.planet-science.com/about_sy/events/jump/measure.html

1 million jumpers managed to get about 1/100th the strength of an average earthquake.

 

[NateTG]

Well, we can do the math:

Let's say we have 1,000,000 ($10^6$) people, and these people have an average mass of 50 kg, and jump 25 cm.

Then that's going to be a total energy of $mgh=10^6 * 5 *10 * 9.81 * .25\approx1.1*10^7J$. (There's some slop in there, but I really could care less.) I think that's roughly equivalent to the chemical energy in a cup of diesel fuel.

 

[Pengwuino]

And of course its spread over... the entire planet

ahahahahhahaha guys!

Look at the "more info" and the "Professor" whos talking about how its done. Its a piece of crap home movie of a guy who, according to google, doesn't even exist! ahahahaha oh god, 200 million morons

 

[CapnMikey]

Alright, so Jump Day is a bust. But we shouldn't give up ridiculous infeasible, potential disastrous schemes! How about this. We get all these 200,000,000 people, get them to jump in their cars with their families (~1800kg per loaded car), and race in the same direction along a specific longitude at 100kph for some amount of time. This would essentially be angular momentum for a hoop and would set the Earth rotating in the opposite direction as long as they remained in motion, right? So:

$$L_{crazies} = m_{crazies}vr \approx (3.6*10^{11} kg)(30 m/s)(6400000 m) \approx 7*10^{19}$$

$$L_{earth} = (\frac{2}{5}m_{earth}r^2)\omega_{earth} = L_{crazies}$$

$$\omega_{earth} \approx 7*10^{-19} rad/s$$

At that rate we could point one of the poles at the sun in under 70,000,000,000 years! Let's go! *jumps in car and speeds northward*

Uh, okay, so there'd probably be some weird gyroscope things happening that would complicate things. Anyways ... Hi!

 

[BobG]

Alright, so Jump Day is a bust. But we shouldn't give up ridiculous infeasible, potential disastrous schemes! How about this. We get all these 200,000,000 people, get them to jump in their cars with their families (~1800kg per loaded car), and race in the same direction along a specific longitude at 100kph for some amount of time. This would essentially be angular momentum for a hoop and would set the Earth rotating in the opposite direction as long as they remained in motion, right? So:

$$L_{crazies} = m_{crazies}vr \approx (3.6*10^{11} kg)(30 m/s)(6400000 m) \approx 7*10^{19}$$

$$L_{earth} = (\frac{2}{5}m_{earth}r^2)\omega_{earth} = L_{crazies}$$

$$\omega_{earth} \approx 7*10^{-19} rad/s$$

At that rate we could point one of the poles at the sun in under 70,000,000,000 years! Let's go! *jumps in car and speeds northward*

Uh, okay, so there'd probably be some weird gyroscope things happening that would complicate things. Anyways ... Hi!

Yeah, there would in a way. You'd get precession. The poles would map out a small circle, but the overall tilt of the Earth would be about the same.

Wait, the Sun already causes precession of the Earth much more effectively than 200,000,000 people, which is why the First Point of Aries currently lies in Pisces or Aquarius (depending upon whether you're an astronomer or an astrologer).