Is World Jump Day Real? A Closer Look at This Controversial Event

[BobG]

The Sun generally appears to rise in the east, and to set in the west. So, which way is the Earth spinning?

Where the heck do you live? In Alaska in the summertime, the Sun rises in the North and sets in the North. So which way is the Earth spinning?

Hmmm, I guess your reply isn't any sillier than the original comment. When I was in Alaska for a year, I did find it odd that when I wanted to look homeward towards Omaha, I had to look due East. Directions are kind of funny when you're so close to the poles.

 

[Aether]

The Sun generally appears to rise in the east, and to set in the west. So, which way is the Earth spinning?

Where the heck do you live? In Alaska in the summertime, the Sun rises in the North and sets in the North. So which way is the Earth spinning?

Ha ha, I said "generally".

 

[SGT]

You misread/hear: earthquakes alter the Earth's rotation, not it's orbit.

The total momentum of the Earth cannot be changed by internal forces. If the rotation of the planet is altered, so is its angular momentum. In order to conserve the total momentum, the orbital speed must be altered.
Something similar has being happening in the last 4 billion years or so. The Moon was closer to Earth and both bodies had a faster rotation.
Friction caused by tides has slowed both rotations in such a way that now the Moon always faces the Earth with the same side. The conservation of momentum of the Earth-Moon system has made the satellite move farther from the planet.

 

[Aether]

You misread/hear: earthquakes alter the Earth's rotation, not it's orbit.

If the rotation of the planet is altered, so is its angular momentum. In order to conserve the total momentum, the orbital speed must be altered.

Incorrect. Angular momentum is a product of rotational inertia and angular speed. The rotational inertia of the Earth decreased significantly as a result of the earthquake that caused the tsunami in Dec. 2004 for example. To conserve angular momentum, the angular speed of the Earth's rotation had to increase proportionally.

 

[russ_watters]

Are you sure about this?

Am I sure about what? Where the energy comes from or what the effect is?

If you are simply saying the effect will be small, I never said it wouldn't be. But it won't be zero, unlike the net effect of the World Jump Day scenario.

nuclear bomb converts a little bit of nuclear mass, , into a lot () of thermal kinetic energy and electromagnetic radiation, . That part of the electromagnetic radiation which leaves the Earth for good does reduce the mass-energy of the Earth a little bit, and therefore it does change the Earth's orbit a little bit (so does shining a flashlight into space ), but AFAIK the force of the explosion per se can not change the Earth's orbit unless it propels some object(s) to escape velocity and they actually leave the Earth so that they aren't part of it anymore.

A flashlight still has a nonzero effect (unlike the World Jump Day effect which is exactly zero), but the image that puts in ones head is a little misleading. Radiation pressure is significant enough that a there have been number of different means of harnessing it proposed to propel spacecraft .

 

[russ_watters]

Incorrect. Angular momentum is a product of rotational inertia and angular speed. The rotational inertia of the Earth decreased significantly as a result of the earthquake that caused the tsunami in Dec. 2004 for example. To conserve angular momentum, the angular speed of the Earth's rotation had to increase proportionally.

I'm not sure if it was a factor for the earthquake or not, but the inertia doesn't even have to change. The rotation of the Earth causes friction, at the very least in the atmosphere and oceans, (not sure about inside the planet, but probably there too), which also slows the Earth's rotation by a measurable amount.

 

[Aether]

Yes, it would. If you're looking to compare that with "World Jump Day", the difference is that the energy of the bombs starts as nuclear energy, not mechanical energy. So there is a net input of mechanical energy.

Are you sure about this?

Am I sure about what? Where the energy comes from or what the effect is?

Are you sure that "...the difference is that the energy of the bombs starts as nuclear energy, not mechanical energy. So there is a net input of mechanical energy". You seem to be implying here that momentum is not conserved in a nuclear reaction. How might "a net input of mechanical energy" from a nuclear reaction influence the orbit of the Earth "unless it propels some object(s) to escape velocity and they actually leave the Earth so that they aren't part of it anymore"?

Incorrect. Angular momentum is a product of rotational inertia and angular speed. The rotational inertia of the Earth decreased significantly as a result of the earthquake that caused the tsunami in Dec. 2004 for example. To conserve angular momentum, the angular speed of the Earth's rotation had to increase proportionally.

I'm not sure if it was a factor for the earthquake or not, but the inertia doesn't even have to change. The rotation of the Earth causes friction, at the very least in the atmosphere and oceans, (not sure about inside the planet, but probably there too), which also slows the Earth's rotation by a measurable amount.

I was agreeing with you there, and disagreeing with SGT.

[add]However, if rotational inertia is constant but angular speed is not, then angular momentum is not conserved and I would agree with SGT that some orbital mechanical process is likely at work.

 

[Pythagorean]

The Sun generally appears to rise in the east, and to set in the west. So, which way is the Earth spinning?

Well, I live in Alaska where the sun just does circles over your head in the summer (practically), but given that description, the Earth rotates towards the East.

 

[russ_watters]

Are you sure that "...the difference is that the energy of the bombs starts as nuclear energy, not mechanical energy. So there is a net input of mechanical energy". You seem to be implying here that momentum is not conserved in a nuclear reaction.

Total energy is conserved, mechanical energy is not because nuclear energy is converted to mechanical energy. The same applies to radiated electromagnetic energy.

How might "a net input of mechanical energy" from a nuclear reaction influence the orbit of the Earth "unless it propels some object(s) to escape velocity and they actually leave the Earth so that they aren't part of it anymore"?

Yes, matter would have to be thrown away from the earth. I'm not sure how much actually is for a nuclear bomb - certainly it would depend on how big it is. Regardless, the radiated EM energy that escapes into space is probably a pretty significant fraction of the total energy.

I was agreeing with you there, and disagreeing with SGT.

I was just expanding on it.

 

[Aether]

Well, I live in Alaska where the sun just does circles over your head in the summer (practically), but given that description, the Earth rotates towards the East.

That's right, but you don't have to rely on that description. As the Sun appears to circle overhead, does it go clockwise or counterclockwise? You could predict the direction based on your earlier conclusion that "the Earth rotates toward the East", and then observe directly which way it goes.

 

[SGT]

Incorrect. Angular momentum is a product of rotational inertia and angular speed. The rotational inertia of the Earth decreased significantly as a result of the earthquake that caused the tsunami in Dec. 2004 for example. To conserve angular momentum, the angular speed of the Earth's rotation had to increase proportionally.

How did the earthquake decrease Earth's rotational inertia? Was matter lost or did the radius of the planet increase?

 

[Aether]

How did the earthquake decrease Earth's rotational inertia? Was matter lost or did the radius of the planet increase?

By tectonic subduction along a tectonic plate boundary. http://usinfo.state.gov/products/pubs/tsunami/earthquake.htm

While it might seem fairly incredible the length of the day is changing all the time -- not by an amount that anyone would notice, but by amoints that are easy to detect instrumentally. The changes are only a few milliseconds (a millisecond is one thousandth of a second) but they are very easy to measure. The record below shows that there are very regular variations and also very irregular variations. All of the changes must in some way be caused by the re-distribution of mass over the surface and with in the Earth. Seasonal changes (curve d) are caused by the change in ice volume and relative amounts of water in the atmosphere from summer to winter. Longer period changes and shorter period changes (curves c and e respectively) are more difficult to explain. Some are caused by the phase of the El Nino -- the Earth rotates differently in an El Nino year than in a La Nina year because these phenomena change the distribution of wet and dry parts of the world. Even longer period changes must be caused by processes in the deep Earth that move masses around such as subduction of large slabs of lithosphere. The cause of many of the longer period signals is not well understood.

http://www.ldeo.columbia.edu/users/jcm/Topic2/Topic2.html

 

[Pythagorean]

That's right, but you don't have to rely on that description. As the Sun appears to circle overhead, does it go clockwise or counterclockwise? You could predict the direction based on your earlier conclusion that "the Earth rotates toward the East", and then observe directly which way it goes.

True enough, but it's still not something that I could tell you without turning 'obsrevation mode' on for a day. I've actually made quite the habit of not looking at the sun (probably because it's there all day and night.) and especially not several times a day to check its position.

 

[Aether]

True enough, but it's still not something that I could tell you without turning 'obsrevation mode' on for a day. I've actually made quite the habit of not looking at the sun (probably because it's there all day and night.) and especially not several times a day to check its position.

Yes, I was hoping that you would turn on 'observation mode' and then report back what you saw.

 

[Pythagorean]

Yes, I was hoping that you would turn on 'observation mode' and then report back what you saw.

I could do that. Today: clouds.

I'll make a note of it though for when it's clear out.