# Question regarding Earth, Moon and tidal forces

1. Nov 18, 2015

### ezach1

1. The problem statement, all variables and given/known data
If the distance between the Earth and the Moon doubled, by what factor would the tidal forces felt on Earth decrease by?

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

3. The attempt at a solution

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...

2. Nov 18, 2015

### stockzahn

3. Nov 18, 2015

### ezach1

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

4. Nov 18, 2015

### stockzahn

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).

5. Nov 18, 2015

### ezach1

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

6. Nov 18, 2015

### stockzahn

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

7. Nov 18, 2015

### ezach1

Ftidal= 2GMearth md/r^3

8. Nov 18, 2015

### 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?

9. Nov 18, 2015

### ezach1

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

10. Nov 18, 2015

### ezach1

swap earth and moon??

11. Nov 18, 2015

### stockzahn

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?

12. Nov 18, 2015

### ezach1

no...i guess back to the drawing board.

13. Nov 18, 2015

### stockzahn

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.

14. Nov 18, 2015

### ezach1

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

15. Nov 18, 2015