Question regarding Earth, Moon and tidal forces

[ezach1]

Homework Statement

If the distance between the Earth and the Moon doubled, by what factor would the tidal forces felt on Earth decrease by?

Homework Equations

Not sure if there are any relevant equations
F = GM1M2 / r∧2

The Attempt at a Solution

[/B]G = 1/d^2, if d is doubled, then G = 1/2^2 = 1/4 The force is 1/4 the original strength.


Im trying guys...

 

[stockzahn]

The tidal forces are proportional to 1/r³, the relevant equation you noted is part of the derivation of the tidal forces. Basically your thoughts are correct, but you took the wrong formula.

Have a look: https://www.physicsforums.com/threads/how-do-you-derive-the-tidal-force-equation.70391/

 

[ezach1]

so the answer is right? but I was suppose to use the roche limit equation?

 

[stockzahn]

so the answer is right? but I was suppose to use the roche limit equation?

No, the answer was wrong, because you based it on the wrong formula, but the idea in your attempt is correct.

You will find the correct formula easily if you look for it in the internet (as well as the derivation).

 

[ezach1]

No, the answer was wrong, because you based it on the wrong formula, but the idea in your attempt is correct.

You will find the correct formula easily if you look for it in the internet (as well as the derivation).

Am I looking for the roche limit equation? or Newtons law?

 

[stockzahn]

Try "derivation of tidal forces" or "tidal force equation"

 

[ezach1]

Try "derivation of tidal forces" or "tidal force equation"

Ftidal= 2GMearth md/r^3

 

[stockzahn]

That would be the tidal force on the moon caused by the earth. Try to adapt it.

And just to be sure: what do r, d and m mean in your equation?

 

[ezach1]

That would be the tidal force on the moon caused by the earth. Try to adapt it.

And just to be sure: what do r, d and m mean in your equation?

r is the radius of the moon, d is the distance, and m is the affected object on the moon??

 

[ezach1]

r is the radius of the moon, d is the distance, and m is the affected object on the moon??

swap Earth and moon??

 

[stockzahn]

r is the radius of the moon, d is the distance, and m is the affected object on the moon??

With this logic the tidal forces would in increase with increasing distance and decrease with increasing size of the moon. Does that seem to be correct?

 

[ezach1]

With this logic the tidal forces would in increase with increasing distance and decrease with increasing size of the moon. Does that seem to be correct?

no...i guess back to the drawing board.
My head is about to explode...

 

[stockzahn]

swap Earth and moon??

Try to write down the formula for the tidal forces caused by the moon on Earth and use unambiguous symbols with correct indices and/or describe them properly.

 

[ezach1]

Try to write down the formula for the tidal forces caused by the moon on Earth and use unambiguous symbols with correct indices and/or describe them properly.

I can't...but thanks for your time and help. It is much appreciated...

 

[ezach1]

I can't...but thanks for your time and help. It is much appreciated...Im slowly realizing that I need help with basic math/algebra. Only then will I be able to understand these equations.