The Moon moving away 1" per year

[Ceti Alpha V]

I read the moon moves away from the Earth at about 1 inch per year. My questions is why? I heared it's something to do with tidal friction, the Earth is slowing down but the moon is increasing in orbital velocity, causing the increase in distance.

Second question, the Earth (and presumable the moon) increase in mass each year due to space debris falling to the surface. Would this increase in mass not increase the gravity and pull the objects closer together?

Ceti

[Struders]

I cant answer the question as such, but I know the moon is moving away from the earth at about 2.5cm a year (thats about the same speed as your finger nails grow).

I am going from memory here, but I think its because of the tidal forces... as you mention an interesting spin off from that is its also making the earth spin slower. Some ancient trees show us that the length of day used to be much shorter, making the number of days in a year was about 400days long (about 320million years ago) cool eh?

[brianb]

I read the moon moves away from the Earth at about 1 inch per year. My questions is why? I heared it's something to do with tidal friction, the Earth is slowing down but the moon is increasing in orbital velocity, causing the increase in distance.

That's exactly right. The angular momentum has to be maintained, if the earth loses angular momentum it has to go somewhere and the moon's orbital motion is where the angular momentum is transferred to.

the Earth (and presumable the moon) increase in mass each year due to space debris falling to the surface. Would this increase in mass not increase the gravity and pull the objects closer together?

The mass increment is infinitesimal & the "random" nature of the arrival means that the angular momentum is scarcely affected.

[Ronseal]

The moon used to be a lot closer, which would cause massive tidal variations, and at the same time the earth was spinning faster - days were around 21hrs about 400m years ago.

The moon orbiting the earth in the opposite direction to earths spin has in fact been slowing it down. The moons gravity acting as a brake on the earths spin so we now have longer days.

I beleive it has been moving away ever since its formation, and will eventually leave , but would this be before the sun turned giant on us? who knows.

The moon leaving or even getting farther away would have big implications to the earths wobble, we could end up tilted pole on to the sun!

There was a programme "Do we really need the moon" on BBC a few weeks ago, try iPlayer but it looks like theres only clips left.

[StevieDvd]

How about to avoid any problems with the moon hetting away, albeit slowly, we declare 1st April World 'Point your magnet at the moon day'? Perhaps we can cut it to 1/2" a year. :-)

[acey]

I read the moon moves away from the Earth at about 1 inch per year. My questions is why? I heared it's something to do with tidal friction, the Earth is slowing down but the moon is increasing in orbital velocity, causing the increase in distance.

The person who first came up with the theory of tidal friction was George Darwin, son of Charles. Eventually the Earth's rotation and the lunar orbital period will be equal: the Moon will appear fixed in space. This tidal-locking is observed in a number of planetary satellites.

Tidal acceleration - Wikipedia, the free encyclopedia

Tidal locking - Wikipedia, the free encyclopedia

George Darwin - Wikipedia, the free encyclopedia

[brianb]

How about to avoid any problems with the moon hetting away, albeit slowly, we declare 1st April World 'Point your magnet at the moon day'? Perhaps we can cut it to 1/2" a year. :-)

If all the Chinese were to run westwards (and keep running) the earth would spin a bit faster ....

[Ceti Alpha V]

Thanks for the replies. If I've got it right, the moon causes the tides and the pull/ friction caused slows the Earth. The moon is pulled to the Earth but due the rotation, never crashes in. As we slow, the angle increases and the moon increases in distance.

If so, if the Earth sped up a bit, the moon would come closer? Would an ice age help or be a neutral factor (in that there would be less liquid sea?)

I like the idea about the magnets, very good ;-)

I'll keep an eye out for that Beeb programme, it may be repeated again on BBC 3 or 4 - and I'll check the links provided.

A lot to this Astronomy game!! :-o

[acey]

The Earth's rotation slows because it's losing energy in the form of heat. The heat comes from the friction of the tides, and the tides are raised by the Moon. If you were to speed up the Earth again it wouldn't affect the Moon's orbit.

[Moonshane]

If all the Chinese were to run westwards (and keep running) the earth would spin a bit faster ....

I once heard that the world's population could fit onto the Isle of Wight - imagine if they did and then all jumped together?

[Nexus 6]

I seem to recollect a very similair post recently

this was on not to long ago and is pretty good

http://topdocumentaryfilms.com/do-we-really-need-the-moon/

[George Jones]

I once heard that the world's population could fit onto the Isle of Wight

Suppose the world's population is 6.4 billion (it is actually a little higher), and that everyone gets a square metre on which to stand. Since 80,000 x 80,000 = 6.4 billion, this would take a square piece of land of 80,000 metres per side, i.e., an 80 kilometre by 80 kilometre square.

imagine if they did and then all jumped together?

The mass of 7 billion people is much, much, much, much, much smaller that the mass of the earth.

[CGolder]

let the Americans do it instead then .... Ouch

[acey]

I once heard that the world's population could fit onto the Isle of Wight - imagine if they did and then all jumped together?

World population: 7 billion

Average mass: 60kg

Total mass: 420 billion kg

Height of jump: 0.5 metre

Potential energy of all those people at high point of jump: 2.1 trillion Joules.

Energy imparted to Earth when they land: 2.1 trillion Joules.

Mass of Earth: 6 trillion trillion kg.

Rebound velocity of Earth when 2.1 trillion Joules is imparted to it (from E = 1/2 m v**2): approx 1 billionth of a metre per second.

I don't think anybody would notice the Earth move. But they'd be very glad to get off the Isle of Wight afterwards!

[Moonshane]

ha ha - imagine getting out of the car park??!!