Earth slowing; time adjusted

[Soutpeel]

Only in Thailand was this a headline

Of course as in the west they publish really "important" headlines, such as Kim Kardashen buys a new handbag...

[sirineou]

Just to clear up any confusion. Leap seconds are added due to the fact that the earth take slightly longer than 24 hours to make a complete rotation. The earth is slowing due to tidal lock, but the slow is not very drastic. Therefore, it needs to be adjusted every so often. If you look at the moon, you always see the same side because it is tidally locked to the earth. Thanks to a molten outer core, plate tectonics, and vast oceans, earth is not yet tidally locked to the sun. Eventually it will be, but we will all be long dead or some kind of robot-human hybrid before that happens.

There is no such thing as centrifugal force. What what an object feels when something spinning is actually a change in momentum which is tangent to a rotating object. The force is pushing towards the center of a rotating body. Otherwise said momentum would carry the object away. This force is called centripetal force. This is easily tested by spinning a ball on a string. The only force exerted is you pulling to the center on a string. When you let go, it flies off tangent to the circle. It's analogous to when you brake a car quickly. You feel yourself move forward, but there is no force pushing forward. Your momentum is carrying you forward and the force of your seat belt or amulet pushes you back into your seat. There was no forward force, just momentum. (okay technically there is a forward force on the bottom of your tires, but that isn't what you feel)

the correct term is angular momentum

where you have two forces pulling in different directions, in this case forward momentum due the earths rotation and a downward momentum due to gravity, a simple vector addition will produce a resultant force at an angle to the two initial forces,

this would be angular momentum

at least that is how I remember my Uni physics, some one more current at this could correct me or ad to my explanation.

[StreetCowboy]

Do you believe that the moon rotates on its axis, and circles the earth, or do you believe that the moon rotates around the axis of the earth?

I'm wishing now I'd disassembled my old Sturmey Archer hub

The moon rotates exactly 360° around its axis when it completes one rotation around the earth, so we see always the same side of the moon.

If I tie a string around a conveniently shaped object - say, this coffee mug, and wing it round my head...

... If I tie a string about an object, say this second conveniently shaped coffee mug, move to the centre of the room, and swing it about my head, how often will it rotate on its axis?

Wouldn't it be better to say it rotates about the centre of rotation, the hand holding the string?

SC

[StreetCowboy]

Do you believe that the moon rotates on its axis, and circles the earth, or do you believe that the moon rotates around the axis of the earth?

I'm wishing now I'd disassembled my old Sturmey Archer hub

The moon rotates exactly 360° around its axis when it completes one rotation around the earth, so we see always the same side of the moon.

If I tie a string around a conveniently shaped object - say, this coffee mug, and wing it round my head...

... If I tie a string about an object, say this second conveniently shaped coffee mug, move to the centre of the room, and swing it about my head, how often will it rotate on its axis?

Wouldn't it be better to say it rotates about the centre of rotation, the hand holding the string?

SC

[sirineou]

Do you believe that the moon rotates on its axis, and circles the earth, or do you believe that the moon rotates around the axis of the earth?

I'm wishing now I'd disassembled my old Sturmey Archer hub

The moon rotates exactly 360° around its axis when it completes one rotation around the earth, so we see always the same side of the moon.

If I tie a string around a conveniently shaped object - say, this coffee mug, and wing it round my head...

... If I tie a string about an object, say this second conveniently shaped coffee mug, move to the centre of the room, and swing it about my head, how often will it rotate on its axis?

Wouldn't it be better to say it rotates about the centre of rotation, the hand holding the string?

SC

????

everything rotates around the center of rotation, what else would it rotate around?

I dont know what you were drinking when you wrote this sentence, but I want some

[StreetCowboy]

Do you believe that the moon rotates on its axis, and circles the earth, or do you believe that the moon rotates around the axis of the earth?

I'm wishing now I'd disassembled my old Sturmey Archer hub

The moon rotates exactly 360° around its axis when it completes one rotation around the earth, so we see always the same side of the moon.

If I tie a string around a conveniently shaped object - say, this coffee mug, and wing it round my head...

... If I tie a string about an object, say this second conveniently shaped coffee mug, move to the centre of the room, and swing it about my head, how often will it rotate on its axis?

Wouldn't it be better to say it rotates about the centre of rotation, the hand holding the string?

SC

????

everything rotates around the center of rotation, what else would it rotate around?

I dont know what you were drinking when you wrote this sentence, but I want some

Zyxel says that the moon circles the earth, and also rotates about its own axis (two separate movements with the same period).

I think it would be easier to describe it as a single rotation about the axis of the earth.

With my coffee cup, which always rotated with the handle facing the centre, I didn't find it convenient to consider the cup rotating on its axis once per revolution.

SC

[sirineou]

The moon rotates exactly 360° around its axis when it completes one rotation around the earth, so we see always the same side of the moon.

If I tie a string around a conveniently shaped object - say, this coffee mug, and wing it round my head...

... If I tie a string about an object, say this second conveniently shaped coffee mug, move to the centre of the room, and swing it about my head, how often will it rotate on its axis?

Wouldn't it be better to say it rotates about the centre of rotation, the hand holding the string?

SC

????

everything rotates around the center of rotation, what else would it rotate around?

I dont know what you were drinking when you wrote this sentence, but I want some

Zyxel says that the moon circles the earth, and also rotates about its own axis (two separate movements with the same period).

I think it would be easier to describe it as a single rotation about the axis of the earth.

With my coffee cup, which always rotated with the handle facing the centre, I didn't find it convenient to consider the cup rotating on its axis once per revolution.

SC

Only if your coffee cup had Irish coffee in it

Only kidding you buddy, personally I dont care what the moon does since I really don't like

cheese.

[Daffy D]

We are told that the universe is expanding, so there is no fixed stationary point.

So all the numbers about rotation are pointless as there is no fixed start and stop point to measure from.

[StreetCowboy]

...

...

????

everything rotates around the center of rotation, what else would it rotate around?

I dont know what you were drinking when you wrote this sentence, but I want some

Zyxel says that the moon circles the earth, and also rotates about its own axis (two separate movements with the same period).

I think it would be easier to describe it as a single rotation about the axis of the earth.

With my coffee cup, which always rotated with the handle facing the centre, I didn't find it convenient to consider the cup rotating on its axis once per revolution.

SC

Only if your coffee cup had Irish coffee in it

Only kidding you buddy, personally I dont care what the moon does since I really don't like

cheese.

Maybe a better analogy would have been achieved by tying string to the wheel nuts of my bicycle wheel, after I had removed it, of course, and spinning that around my head, but the likely damage doesn't bear thinking about. That's probably one that's best done outside in the open air.

[tominbkk]

Pretty soon we'll need bigger clocks.

[Zyxel]

StreetCowboy, from the earth the moon does not seem to rotate on its axis but looking from let's say the sun it definitely rotates one turn on its axis in about 28 earth days.

Edited June 17, 2015 by Zyxel

[IMA_FARANG]

The earth has a Moon.

The theory is that a billion or more years ago an asteroid smashed into the Earth and mass was ejected to create he Moon.

The Moon was then much closer in it's orbit and the Moon has moved outward in it's orbit over that period.

The tidal drag with the Moon has slowed the rotation speed of the Earth since then as the Moon has moved outward in it's orbit around the Earth.

The rotation of the Earth has become synchronized with the Earth's rotation. which is why we on the Earth see only one side of the Moon.

As the Moon moves outward in it's orbit around the Earth the tidal Drag on the Earth is very gradually slowing the Earth's rotation also.

Be glad we on earth have the Moon with a 24 hour day not the original 8 hour rotation period when the Moon was ejected and began to form from the fragments of the earth's crust.

Otherwise it's quite possible life would never have survived.

[BritTim]

The earth has a Moon.

The theory is that a billion or more years ago an asteroid smashed into the Earth and mass was ejected to create he Moon.

The Moon was then much closer in it's orbit and the Moon has moved outward in it's orbit over that period.

The tidal drag with the Moon has slowed the rotation speed of the Earth since then as the Moon has moved outward in it's orbit around the Earth.

The rotation of the Earth has become synchronized with the Earth's rotation. which is why we on the Earth see only one side of the Moon.

As the Moon moves outward in it's orbit around the Earth the tidal Drag on the Earth is very gradually slowing the Earth's rotation also.

Be glad we on earth have the Moon with a 24 hour day not the original 8 hour rotation period when the Moon was ejected and began to form from the fragments of the earth's crust.

Otherwise it's quite possible life would never have survived.

The giant impact hypothesis for the creation of the moon requires an impact from something a lot bigger than a regular asteroid, in fact something about the size of Mars. It is worth noting that, while the giant impact hypothesis will probably end up being correct, it is not proven. Indeed, certain anomalies exist that are difficult to explain.

[natway09]

The article is not written well?

I do not know why they even bother to tell you about it.

Please write it better in Thai , I look forward to hearing

Leave these people alone!!!!

[canman]

Along similar lines of things orbiting other things. Why does an astronaut appear to be weightless relitive to the inside of the shuttle?

For example if you were able to build a tower up the the height of the shuttle orbit and stand on the top of said tower you would not be weightless, you would weigh something like 80% of your weight on the ground. I understand enough about orbital mechanics to know the answer, just a teaser for some who may not. The answer ties in with the discussion on angular momentum

Edited June 17, 2015 by canman

[canman]

Pretty soon we'll need bigger clocks.

I always wanted a bigger clock.

*Edited for spelling*

[hawker9000]

So do we in the UK see the same image as seen in Thailand?

Yes, just not at the same time. The same side/surface area of the moon is always presented to the earth, but not so the earth's surface to the moon. Somebody correct me if I'm wrong, but if you were standing on the side of the moon facing the earth, you'd never see the earth "rising & setting" the way we see moonrise & moonset on earth. But if you were watching continuously, and closely enough, you would notice the earth's rotation. (All this not taking into account lightness & darkness.)

[StreetCowboy]

Along similar lines of things orbiting other things. Why does an astronaut appear to be weightless relitive to the inside of the shuttle?

For example if you were able to build a tower up the the height of the shuttle orbit and stand on the top of said tower you would not be weightless, you would weigh something like 80% of your weight on the ground. I understand enough about orbital mechanics to know the answer, just a teaser for some who may not. The answer ties in with the discussion on angular momentum

You'd want to duck whenever the spaceshuttle came past, though.

If you built your tower up to the same height as geostationary satellites*, you'd be "weightless" in the penthouse, but I can't see you getting planning permission for that.

* so long as you built it on the equator

[Zyxel]

Along similar lines of things orbiting other things. Why does an astronaut appear to be weightless relitive to the inside of the shuttle?

For example if you were able to build a tower up the the height of the shuttle orbit and stand on the top of said tower you would not be weightless, you would weigh something like 80% of your weight on the ground. I understand enough about orbital mechanics to know the answer, just a teaser for some who may not. The answer ties in with the discussion on angular momentum

You have to turn around the earth at at least 11km/s (I think) to generate enough centrifugal force to compensate for the force of gravity. At the top of the tower you will not go fast enough to be weightless but you will be lighter. In your example the shuttle is moving faster than the top of a tower at the same height.

[sirineou]

Along similar lines of things orbiting other things. Why does an astronaut appear to be weightless relitive to the inside of the shuttle?

For example if you were able to build a tower up the the height of the shuttle orbit and stand on the top of said tower you would not be weightless, you would weigh something like 80% of your weight on the ground. I understand enough about orbital mechanics to know the answer, just a teaser for some who may not. The answer ties in with the discussion on angular momentum

Because they are both falling at the same rate .

"Learning how to fly is easy, simply throw your self at the ground and miss" I believe the line is from the Hitchhikers Guide to the Universe , anyway in the above line is a hint why satellites don't crush in t the earth

[Yunla]

On my Gobots watch the little-hand is now pointing at Cy-Kill, which means its time for my coffee. I don't know if this includes the rogue seconds in the OP. This lost second affects us all.

[northernphil]

I didn't realise that S.'awkins had so many nom de plumes. So tell me ...is a short time shorter or longer or does that depend more on the angle of dangle ?

[rubl]

The end is near, the end is near

"The last time a second needed to be added to the day was on June 30, 2012. For Qantas Airlines in Australia, it was a memorable event. Its systems, including flight reservations, went down for two hours as internal system clocks fell out of synch with external clocks."

http://www.informationweek.com/software/information-management/leap-second-clocks-in-on-june-30/d/d-id/1320850

[exbikey]

The end is near, the end is near

"

Too bloody right according to programme I saw on Discovery Channel last night.

They reckon in around 4billion years The Milky Way (our galaxy) is going crash in to the galaxy Andromeda ( or was it Andromeda going to crash in to us?), then it's curtains.

So all this worry about the Earth slowing is a waste of time.

Honestly, couldn't sleep last night worrying about it. Now, do you think it worth me renewing my gymn membership?