Question

Is the earth's rotation slowing down?

Asked by: Mallory Thomson

Answer

Yes it is, due to a transfer of Earth's rotational momentum to the Moon's orbital momentum as tidal friction slows the Earth's rotation. That increase in the Moon's speed is causing it to slowly recede from Earth (about 4 cm per year), increasing its orbital period and the length of a month as well.

To picture what is happening, imagine yourself riding a bicycle on a track built around a Merry-go-Round. You are riding in the same direction that it is turning. If you have a lasso and rope one of the horses, you would gain speed and the Merry-Go-Round would lose some. In this analogy, you and your bike represent the Moon, the Merry-Go-Round is the rotating Earth, and your lasso is gravity. In orbital mechanics, a gain in speed results in a higher orbit.

The slowing rotation of the Earth results in a longer day as well as a longer month. Once the length of a day equals the length of a month, the tidal friction mechanism will cease. (ie. Once your speed on the track matches the speed of the horses, you can't gain any more speed with your lasso trick.) That's been projected to happen once the day and month both equal about 47 (current) days, billions of years in the future. If the Earth and Moon still exist, the Moon's distance will have increased to about 135% of its current value.

Answered by: Paul Walorski, B.A., Part-time Physics Instructor


Answer

The Earth's rotation is slowing down from rotational energy transfer to the moon's orbit through tides. The moon is very slowly increasing its orbital radius.

http://en.wikipedia.org/wiki/Tidal_acceleration

Every 18 months on the average, with variation, a leap second is added to planetary time keeping to keep the day consistent with atomic clocks and astronomical observations.

The next leap second will be at the end of December 2005. The one before that was December 1998.

http://tycho.usno.navy.mil/leapsec.html
http://en.wikipedia.org/wiki/Leap_second

Answered by: Uncle Al, Irvine, CA

Search

Loading






Science Quote

'The true spirit of delight, the exaltation, the sense of being more than Man, which is the touchstone of the highest excellence, is to be found in athematics as surely as in poetry.'

Bertrand Russell
(1872-1970)
Science Sidebar | Science Education Articles
Cool Summer Science Projects

Why not make science a part of your family’s summer? Perhaps you can set aside one day a week for outdoor projects—maybe Mad Scientist Monday or Scientific Saturday? Here are a few ideas to help get you started. Continue reading ...

10 Ways to Keep Your Kids Interested In Science

Young children are natural scientists: they ask questions, pick up sticks and bugs outside, and are curious about the world around them. But as they get a bit older, many kids gradually lose their interest in science. They might see it as just another task at school, something that doesn't apply to their lives. Of course nothing could be further from the truth, so here are ten ways you can remind your kids that science is everywhere. Most of these are fun for adults, too! Continue reading ...

Top Selling

Here are our physics & astronomy bestsellers:
Magnetic Levitator - Classic
3D Magnetic Field Tube
KonusScience 5 Way Microscope Kit
Periscope
Revolving Multi-Color Fiberoptic Light
Tin Can Robot 4M Kit
Potato Clock 4M Kit
Mini Plasma Ball
Clean Water Science 4M Kit
Solar Radiometer

Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department