Why does the earth occasionaLLy increase it's rotation speed?

Question

in this Link http://en.wikipedia.org/wiki/Leap_second under "Announcement of leap seconds" it taLks about negative Leap seconds, if the earth's rotation shouLd become sLightLy faster, so my question is how couLd that happen?

Answer 1

In my logic, it might be due to the inter-system bodies getting closer to each-other, due to the pull of the sun and themselves between each-other.
The closer the proximity of two bodies between one-another is, the more effect the gravitational energy between the two will be stronger.

Answer 2

Well, the first way to notice the end result of this effect is to look at the moon. The moon orbits the earth every 28 days, and it also rotates once every 28 days. This was caused by the gravitational field of the Earth and the Sun as the moon evolved.

The Earth is much larger than the moon, so this effect takes much longer to develop (hundreds of billions of years), but would in theory happen. Eventually, due to the gravitational effects of the moon and Sun, the Earth will eventually take 1 year to rotate, the same as our orbital period.

This explains why it slows down gradually.

The Earth could, in theory, speed up its rotation if other tidal gravitational effects came into play. For example, a large comet passing close to the Earth could produce a small tidal effect and speed up the Earth's rotation.

Something like this has never been documented, and it is unlikely that anything will happen which will require the need for a negative leap second.

This sounds more like a contingency; a case of "if there's positive, there must be negative" kind of thing.

Answer 3

No negative leap second has ever been needed. The wikipedia article only says that, "Negative leap seconds are also possible should the Earth's rotation become slightly faster", but it does not say that this has ever happened or is ever expected to happen.

However, I can imagine a couple ways Earth's rotation speed could increase. A large volcano could blow off its top few thousand feet. This would move some of the Earth's mass closer to the center and cause rotation to speed up, like the ice skater pulling her arms closer to her body to spin faster. Or an asteroid could hit a glancing blow in a direction that adds to the Earth's rotation speed.

Answer 4

I dont know if it does so on occasion. One thing that measurably did speed up the earths rotation was the 12-25-2004 sumatra earthquake that cause the destructive tidal waves in that region. the earths rotational speed is slowing due to the gravitation effects of the moon. So in about 2 billion years a day on earth will last 36 hours or so

Answer 5

I think it's only theoretical:
"Although it is possible to have a negative leap second (a second removed from UTC), so far, all leap seconds have been positive (an extra second has been added to UTC). Based on what we know about the earth's rotation, it seems unlikely that we will ever have a negative leap second."

http://tf.nist.gov/timefreq/general/leaps.htm