Gravitation in the solar system (1 Viewer)

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Let's say, in an hypothetic situation, that the moon would explode to tiny bits.

What would happen to the earth?

I was said it would actually change:

The orbit of the earth *duh!*
Water levels all around the world *duh!*

And the point I have a problem with is this last one...

It will change the earth's rotational speed, this derived from the fact that the moon goes around the earth at the same speed than the earth revolves upon it's own axis... Is this true, or totally fallacious?

The person in question also mentioned studies regarding this possible fallacy...
 

ZapperZ

Staff Emeritus
Science Advisor
Education Advisor
Insights Author
2018 Award
34,612
3,538
First we have the sun-exploding thread. Now we have the moon-exploding thread. What's with all this all of the sudden? Is someone running a crackpot website and posting all of these questions, while you guys bite the bait?

Zz.
 

DaveC426913

Gold Member
17,752
1,501
"...the moon goes around the earth at the same speed than the earth revolves upon it's own axis..."

Think about this for a second. If the Moon overhead were orbiting at the same speed as the Earth rotates below, then the Moon would always hover over the same spot on Earth.

Does it? No. The Moon is in a different place overhead (and sometimes not at all) every day.

You should tell your friend to shut up until he knows what he's talking about.
 
DaveC426913 said:
"...the moon goes around the earth at the same speed than the earth revolves upon it's own axis..."

Think about this for a second. If the Moon overhead were orbiting at the same speed as the Earth rotates below, then the Moon would always hover over the same spot on Earth.

Does it? No. The Moon is in a different place overhead (and sometimes not at all) every day.

You should tell your friend to shut up until he knows what he's talking about.
*chuckle* Aye, that was about what I was going to tell him. hehe
 
Hold on, doesn't the Moon affect the Earth's rotation rate anyway?
Isn't it slowing down as the Moon moves further away from us?
(Fossils show the Earth's day was much shorter in prehistoric times when the Moon was closer.)
 
Earth's rotation rate, and Moon's orbit are gradually synchronising.
It's called 'tidal locking'
The Moon is already tidally locked to the earth (we always see the same face of the Moon, all but a slight rocking - called 'libration')

I suppose if the Moon were suddenly vapourised, then the Earth's rotation would stop slowing.

But it ain't gonna happen.........
 
So the moon DOES affect the earth's rotational speed?
 

SpaceTiger

Only Cat With a Helmet
Staff Emeritus
Science Advisor
Gold Member
2,917
1
Neohaven said:
So the moon DOES affect the earth's rotational speed?
Yes, it slows it down very slowly, but if you remove the moon, the rotation speed will not suddenly change, it will just stop slowing down.
 

LURCH

Science Advisor
2,530
106
Just for perspective; the Moon's gravitational "drag" slows the Earth's rotation by about 1.5 milliseconds per century. it takes a hundred million years for the Earth's "day" to get a second-and-a-half longer. If this deceleration were to cease, then a hundred million years from now a day will be just as long as it is today, rather than 1.5 seconds longer.

We live with this deceleration every day of our lives. However, if it were to suddenly dissapear, I don't think anyone would fall over! Of course, here in Michigan, we just moved our clocks back one hour yesterday (Sunday); I wonder if that would get messed up?
 

Office_Shredder

Staff Emeritus
Science Advisor
Gold Member
3,718
98
If the moon exploded, by conservation of momentum, the center of mass of the moon would remain in the same place. So there would be no net effect

:P

(For a little while at any rate...)
 
14
0
Well, if the earth rotation slows down for about 1.5 milliseconds(1.5x10^-3 sec; per day) in one century it would take 100.000 years(1000 centuries) until the day would be 1.5 seconds longer.
 

LURCH

Science Advisor
2,530
106
Ooops! You're absolutely right, sstone. I missplaced my decimal, did microseconds instead of milliseconds; one hundred thousand years is the correct figure not one hundred million.

Thanks for catching that.
 

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top