# Where does Gravitation equals zero?

1. May 7, 2013

### Sapphiretwirl

1. The problem statement, all variables and given/known data

So a 1kg mass and a 2kg mass are placed 10m away from eachother, somewhere in between them the force of gravity cancles out. Where would am object with a mass of m be placed so that it is not affected by either of the 1kg and 2kg masses?

2. Relevant equations

Not sure, something with gravitation,rotational motion, angular velocity Ect.

3. The attempt at a solution

F=G*m1(m)/r

2. May 7, 2013

### Staff: Mentor

Your formula is not quite right; see: Gravity

All you need to worry about is the force of gravity. Hint: Will the ƩF = 0 point will be closer to the 1 kg mass or the 2 kg mass?

3. May 7, 2013

### Sapphiretwirl

The 1 kg mass of course, but I don't know where to go from there :(

4. May 7, 2013

### Staff: Mentor

Good!

Call the distance to the 1 kg mass "x". What is the force of gravity from the 1 kg mass at that point?

If the distance to the 1 kg mass is x, what would be the distance to the 2 kg mass? What is the gravitational force from the 2 kg mass at that point?

Solve for the distance that makes the net force zero.

5. May 7, 2013

### Sapphiretwirl

I've tried but I can't solve for the distance, the furthest I've gotten is this

Fg=G*(m1(m2))/r^2

0=6.67*10^-11(2/x^2)

6. May 7, 2013

### Office_Shredder

Staff Emeritus
Isn't it a bit weird that your formula for the force of gravity doesn't involve the mass m of the object we are looking at?

There are two sources of gravity, each of them acts on the object in a different direction.

7. May 7, 2013

### Sapphiretwirl

I got 1.7 meters for x

8. May 7, 2013

### Sapphiretwirl

I probably did something wrong

9. May 7, 2013

### haruspex

Pls post your working, not just the numeric answer. Preferably, do all the working in symbols, only plugging in numbers at the end. Follow Doc Al's recipe.

10. May 7, 2013

### Sapphiretwirl

I really don't know what I did

11. May 7, 2013

### haruspex

Then start again, following Doc Al's recipe. Answer each question in turn, as far as you can: