If we need to add leap seconds at a constant rate of one every 2 years this would show how much deceleration of earth's rotational velocity?

Answer 1

No. It is a misunderstanding that regular addition of leap seconds is directly related to the continuing deceleration of Earth's rotational velocity.

There is a connection, but it's not a simple one.

It's mainly because of how "seconds" of time have been defined.

Think of it this way. There is a perfectly accurate clock on your wall. You own a wrist watch that runs at a very constant rate, but it loses one second per year. You set your watch to the perfectly accurate clock, and notice a year later that you must set your watch again, and you set it ahead one second, to match your clock. Again the following year you must do it again. Does the need to do this every year mean that your watch is getting slower? No, it does not mean your watch is getting slower. It means your watch is running at a constant rate, but that the rate is slightly slower than the reference clock on your wall.

The Earth is in fact slowing down very slightly, but not nearly by as much as one second every two years.

"Coordinated Universal Time", which our clocks are now based on, has gone a little out of synchronisation with the rotational period of the Earth. It is very much the same situation as described above. This is what the addition of leap seconds corrects.

See "related links" for more details. The first paragraph in the second link is a good

starting point.