# Derive an Expression

1. Oct 17, 2005

### thursdaytbs

I'm asked to derive the mathematical expression for the erlationship of centripetal force as a function of T, m, and R.

I've found, from data, that F=0.615/T^2 = 0.05m = 1/4R
how would I bring it all together to form one equation involving T^2, m, and R?

Any help, thanks.

2. Oct 18, 2005

### Diane_

I'm not following this exactly. You are asked to derive an empirical formula from data, presumably taken in lab, for centripetal force as a function of period, mass and radius?

You'd need data that holds two of the variables constant while allowing the third to change, and you'd need that from all three variables. Presumably, you can determine then the dependence of centripetal force on each variable. For instance, if you double the mass and hold everything else constant and you find that you have to double the force, then you know that centripetal force is linear in mass. If you double the period and hold everything else constant and you find you have to cut the force to 1/4, then you know that centripetal force has an inverse square dependence on period. All you have to do is find the dependence of each of the variables, then write the equation.

For instance: suppose you find a direct dependence on the cube of the mass, an inverse square dependence on the period and an inverse dependence on the radius. Your equation would then be

F = k m^3/(R T^2)

The k is a proportionality constant, which you would determine from your data once you knew the dependences of the other variables.

If I've misunderstood your question, then this is useless to you. Did it help at all?