| Term: | Tidal friction |
| Definition: |
The friction exerted on a primary body (Earth) because of the phase lag between the tides and the gravitational attraction of the secondary body (Moon). The Earth's rotation is faster than the Moon's orbital motion; therefore the Earth's tidal bulges lead the Moon on its orbit. This has two important effects: The Earth is being pulled slightly 'back' from its sense of rotation. So the Earth's rotation slows (by about 1 second every 50,000 years). Moreover, the Moon is being pulled slightly 'forward' on its orbit. So it is harder for the Earth to hold it in place, and it moves further away from the Earth (by about 3-4 cm per yr). Tidal friction tends to synchronize the rotation period of a close-in companion with the period of its orbital motion around the primary. |