# Shape of lumps

1. Sep 1, 2015

### Gayle

I was solving for a shape on earth which has minimum potential energy. i used method of variation calculus.
I assumed a function f(x) and rotated it around Y axis. sorry for uploading the problem in word.

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2. Sep 1, 2015

### DEvens

What direction does gravity point in?

3. Sep 4, 2015

### Gayle

along negative y direction

4. Sep 4, 2015

### DEvens

I was hoping it would be enough of a hint for you.

Gravity points towards the centre of the mass, not in the y direction. So as you go along the surface the direction of gravity changes.

In other words, you have the wrong formula.

Also, check your formula for potential energy.

5. Sep 4, 2015

### nasu

That shape will be a thin layer spread on the surface. Unless you consider some material going in holes under the surface.

6. Sep 6, 2015

### Gayle

Dear DEvens
i assumed a random curve so how to find the center of mass if i don't know in what geometry the mass is distributed

7. Sep 6, 2015

### Gayle

i am sorry i understood what u meant i will workout the problem and let u know the answer.
thanks for u help