# Kinetic mass?

1. May 16, 2013

### Smelly Eggs

Hi.

I need to find the mass (relativistic mass?) Of an object in rotation.

Say I have a string with a small rock tied to the end.

The relevant variables are:

A) The circumference of the weights path.

B) The weight of the rock itself.

C) The revolutions per minute that B travels around A.

Now, what is the equation needed to put these together to tell me how much 'weight' in kg the spinning rock will exert or pull on the string? Or in other words, how do we know the amount of centripetal force (In kg) the string requires to hold to the spinning rock?

2. May 16, 2013

### rock.freak667

3. May 17, 2013

### Smelly Eggs

Yes, that's exactly what I'm talking about!

The only thing is I don't know any physics so I don't understand those equations.... I just want to know where to put the 3 variables I mentioned to get the outcome I mentioned.

Don't need to know any vertical gravity components or anything like that... just the 3 I menttioned, without concern for gravity or air resistance etc.

Cammon... this should be pretty simple for you physics guys!:tongue: