Answer Moon's Spin: Effects on Earth? | 9yo daughter's Q

[mallaky]

Hello Physics Forums, this is my first thread here.

My daugher of 9 years is getting interested in the moon and tides and those things.
And she askes me a peculiar question which I could not answer. It goes as follows:

If you put a strong rockets on the moon which turn/spin it on the spot, without moving it in any other way, would we feel it on earth/ would it have an effect on the earth? ("or would it just look pretty?")

If anybody could answer that in a basic way it would be much, much appreciated.

Thanks in advance!
(English is 2nd language, so please excuse mistakes)
(edit: I hope this is right forum for this kind of question)

 

[dreamLord]

Just a vague guess, but currently the periods of rotation and revolution for the Moon are the same, which is why we always see '1 side' of the Moon. If you were to increase (or decrease) the period of rotation, then we would see different sides of the Moon on different days. Also, the radius of the Moon's orbit will increase, making it look smaller.

Just my guesses, please don't read too much into them.

 

[mallaky]

Yes, that is what her question means. Attach rockets to the moon which would make it rapidly spin. So we would see all the faces of the moon in maybe one night. Or more, or less. Her question was if that spinning would make tides or have any effect on Earth or not. Maybe i didnt understand your answer?

 

[256bits]

Here is a site about tidal locking which you can use to explain to your daughter of how the moon-earth system interacts to conserve angular momentum, with the moon slowly drifting farther in its orbit from the Earth and the Earth period of rotation becoming slower and slower, until a time will come much farther into the future where the moon and Earth will present to each other the same face continiously.
http://csep10.phys.utk.edu/astr161/lect/moon/tidal.html

If you attach rockets to the moon to make it rotate or spin faster, which is a great idea, by the way, the immediate affect would not be anything different from yesterday. Tides would be the same. Over the course of billions of years, the tidal locking for the earth-moon could take a billion of so years longer. In the meantime, the moon's temperature would increase slightly over time due to the flexing of its surface being raised and lowered. The moon would have tides as well.

I guess someone could hopefully answer the affect long term if you spin the moon clockwise or counterclockwise since I am short of time to think about that right now.

 

[pmacias]

Hi there,

That's a great question from your daughter! The short answer is yes, it would have an effect on Earth.

To explain this further, we need to understand a bit about how the moon's spin and gravity works. The moon is constantly spinning on its axis, just like Earth, but it takes about 27 days for it to make one full rotation. This is why we always see the same side of the moon facing us.

Now, if we were to put strong rockets on the moon and spin it on the spot, it would change the distribution of mass on the moon. This means that the moon's gravitational pull on Earth would also change, albeit very slightly.

This change in gravitational pull would have a small effect on Earth's tides. Tides are caused by the moon's gravitational pull on Earth's oceans. So, if the moon's gravitational pull changes, it would also affect the tides.

However, the effect would be very small and probably not noticeable to most people. Also, the moon's spin is already very stable and any changes to it would likely be corrected by the moon's own gravity.

So, to sum it up, yes, spinning the moon on its spot would have an effect on Earth's tides, but it would be very small and probably not noticeable to us. And it definitely wouldn't just look pretty, it would have a real physical effect!

I hope this helps to answer your daughter's question. Keep encouraging her curiosity and interest in science!