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Timoothy
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If the Earth suddenly disappeared. and the moon started to travel in a straight line instead of its orbit of earth, would the moon continue to rotate on its axis every 27.3 days?
Timoothy said:If the Earth suddenly disappeared. and the moon started to travel in a straight line instead of its orbit of earth, would the moon continue to rotate on its axis every 27.3 days?
tiny-tim said:Hi Timoothy! Welcome to PF!
Yes.
It would orbit the sun, of course, but its angular velocity would stay the same.
It is very difficult to change the angular velocity of a planet or satellite without actually colliding with it!
(You can make it lose energy through tidal forces, but that's about it.)
Timoothy said:Well I've been talking to some people who say that since the moon is in a tidal-lock with earth, it doesn't rotate on its internal axis …
They're wrong. It does. It rotates on its axis every 27.3 days. Earth disappearing will not make that suddenly stop.Timoothy said:Hi, and thanks for the welcome.
Well I've been talking to some people who say that since the moon is in a tidal-lock with earth, it doesn't rotate on its internal axis,
tiny-tim said:Timoothy, the rotation of the moon is a matter of geometry, not physics.
It quite obviously rotates (on an external axis by the way , not an internal one)!
The Moon would proceed to rotate about its own (internal) axis.Timoothy said:So after Earth disappeared and the moon continues to rotate on an "external" axis every 27.3 (earth) days as it orbits the sun, would this "external" axis be closer to the moon or the sun?
DaveC426913 said:They're wrong. It does. It rotates on its axis every 27.3 days. Earth disappearing will not make that suddenly stop.
DaveC426913 said:The Moon would proceed to rotate about its own (internal) axis.
I'm not sure how conservation of momentum would be preserved. Presumably, the disappearing Earth would take its momentum with it.
russ_watters said:You could use the example of a ball on a string. If you swing it around your head, then release it, it will fly off in a tangent and continue to rotate at the same rate it was rotating when you were swinging it around your head.
Timoothy said:One of the arguments I've heard in favor of a moon that does not rotate on its internal axis is, since the moon is in a tidal-lock with earth, it does rotate on an axis during its orbit of earth, but this axis is the (barycenter), which is external, therefor the moon does not rotate on an internal axis.
I understand there's a barycenter, but i just can't imagine how the same side of the moon always faces Earth during its orbit of earth, unless the moon does rotate on its internal axis 1 time during its orbit of earth.
A problem with this argument is that it neglects the fact that the Moon does not keep exactly the same face pointing at the Earth thoughout its orbit. The Moon's orbit around the Earth is slightly elliptical. As such its orbital speed varies as it moves in and out from the Earth. At perigee it takes less time for the Moon to cross 1 degree of the sky than it does at apogee. The Moon's rotation around its axis however is constant. It takes the same amount of time to rotate 1 degree through all points of its orbit. So the Moon, from the Earth, appears to rock slowly side to side a little so that we end up seeng a little more than half the Moon's surface. (this motion is called libration).Timoothy said:One of the arguments I've heard in favor of a moon that does not rotate on its internal axis is, since the moon is in a tidal-lock with earth, it does rotate on an axis during its orbit of earth, but this axis is the (barycenter), which is external, therefor the moon does not rotate on an internal axis.
tiny-tim said:Hi Timoothy!
You're quite right … it is an external axis!
But that doesn't matter … the angular momentum is conserved irrespective of the axis … remember the pipe on the string spinning about an external axis first, then about an internal axis!
Yes, I saw the thread after I posted the previous post. I don't like the way you worded it here, though. You should simply say that the pipe did not start to rotate when released, it merely continued to rotate when released. That stuff about the velocity of the leading and trailing edges is just going to confuse you. It is unnecessary. From your above post, it is really better to model the pipe's motion as two separate motions. I believe someone explained this in your other thread. One motion has the pipe modeled as a point mass, revolving around you, attached to the string. The other motion is the pipe's rotation around its axis. Using this method, it is easy to see that the two motions need not be considered one motion and if one is discontinued (ie, by releasing the string), the other need not also be discontinued. The same principle applies to the moon.Timoothy said:I actually did that experiment a couple of days ago with a two foot length of steel pipe with the string attached to one end of the pipe, and I was surprised that it started to rotate the instant I released the string, but just while ago I read the explanation for it in a different thread, and I now understand the velocity of the leading edge of the pipe was greater than the trailing edge, causing it to continue to rotate when the string was released.
If Earth were to suddenly disappear, the Moon would continue to orbit around the Sun and would not be affected by Earth's absence. However, the Moon's orbit may become more elliptical due to the lack of Earth's gravitational pull.
No, there would not be tides without Earth. Tides are caused by the gravitational pull of the Moon and Sun on Earth's oceans. Without Earth's presence, there would be no tides.
The disappearance of Earth would not have a significant impact on the other planets in our solar system. The gravitational pull of Earth is relatively small compared to the other planets, so their orbits would not be affected.
The Moon does not have a significant atmosphere like Earth, so its atmosphere would not be affected by Earth's disappearance. However, without Earth's magnetic field, the Moon's atmosphere may be more vulnerable to solar winds and radiation.
It is highly unlikely that life could survive on the Moon without Earth. Earth provides essential resources for life such as oxygen, water, and a stable atmosphere. Without these resources, it would be difficult for any form of life to survive on the Moon.