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energyfield775
2016-Aug-30, 02:40 AM
Okay, so if rotation does not cause gravity, and mass does correct? rotation is artificial gravity correct? How come our moon does not rotate, and at what distance would it have to be to be buy gravitational friction reformation, as Saturn like rings of dust around earth?

Swift
2016-Aug-30, 12:34 PM
Hi energyfield775, welcome to CQ.

I've moved your two threads from Moon Mappers to Q&A. Since neither of your threads is about the Moon Mappers program, this seems more appropriate.

Reality Check
2016-Aug-31, 04:37 AM
That is correct energyfield775: rotation does not cause gravity. A rotating body is one that is spinning around an axis so there are forces that are only caused by the spinning. Think of being on a roundabout (https://en.wikipedia.org/wiki/Roundabout_(play)) and feeling the rotation pushing you off it. If you have a ring rotating in space and stand on its inside then the rotation will push you onto the ring surface. This is a rotating wheel space station (https://en.wikipedia.org/wiki/Rotating_wheel_space_station).

The Moon does rotate. It rotates once a day so that it presents one face to the Earth. This is known as tidal locking (https://en.wikipedia.org/wiki/Tidal_locking).

"gravitational friction reformation" sounds like the Roche limit (https://en.wikipedia.org/wiki/Roche_limit) which is 9,492 kilometers for the Moon treated as a rigid body.

VQkr
2016-Aug-31, 06:48 AM
That is correct energyfield775: rotation does not cause gravity. A rotating body is one that is spinning around an axis so there are forces that are only caused by the spinning. Think of being on a roundabout (https://en.wikipedia.org/wiki/Roundabout_(play)) and feeling the rotation pushing you off it. If you have a ring rotating in space and stand on its inside then the rotation will push you onto the ring surface. This is a rotating wheel space station (https://en.wikipedia.org/wiki/Rotating_wheel_space_station).

The Moon does rotate. It rotates once a day so that it presents one face to the Earth. This is known as tidal locking (https://en.wikipedia.org/wiki/Tidal_locking).

"gravitational friction reformation" sounds like the Roche limit (https://en.wikipedia.org/wiki/Roche_limit) which is 9,492 kilometers for the Moon treated as a rigid body.

Bold added. To be clear, that's once per lunar day, which is the same amount of time as about 29 earth days.

Jeff Root
2016-Aug-31, 04:32 PM
The Moon's day is actually longer than its orbital period. It makes a
complete orbit around Earth with respect to the fixed stars in about
27.3 Earth days (its sidereal period), and that is also its rotation period.
But because the Earth and Moon are orbiting the Sun, it takes slightly
longer for the Moon to show the same phase to Earth, about 29.5 days
(its synodic period), which is the length of the lunar day. A difference
of about 2.2 days.

Earth's day is longer than its rotation period for the same reason.
Earth's rotation period is 23 hours, 56 minutes, 4 seconds, while its
day is 24 hours on average, a difference of almost 4 minutes.

-- Jeff, in Minneapolis