Welcome to PhysLink.com - Your physics and astronomy online portal. Stay a while! Check out our extensive library of educational and reference materials. Also, check out our fun section!
What will be the fate of our moon? Will it remain in a stable orbit, crash back into Earth or drift off into space?
Asked by: Tom Burke
The Moon is gradually receding from the Earth, at a rate of about 4 cm per year. This is caused by a transfer of Earth's rotational momentum to the Moon's orbital momentum as tidal friction slows the Earth's rotation. That increasing distance means a longer orbital period, or 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 would 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 distance will have increased to about 135% of its current value.
Answered by: Paul Walorski, B.A., Part-time Physics Instructor
Super Science Magnet Kit
Today's Price: $18.00
Exciting magnet exploration for ages 8 and up! Buy it now! Deal ends at midnight!
Here are our physics & astronomy bestsellers:
Solar Science Kit
Mini Plasma Ball
Deluxe 3D Mirascope
Revolving Multi-Color Fiberoptic Light
Deluxe Water Rocket Set
Solar System Planetarium 4M Kit
Worlds Strongest Magnets
Potato Clock 4M Kit
Windmill Generator 4M Kit
Ultimate Chemistry Set CHEM C3000 v2.0