# Derivation of r (radius) in terms of f (frequency)? Help please.

by BLZ
 P: 3 Okay, so the job I need to do is derive an equation for the radius of an object in terms of its frequency. These are the equations that we are allowed to use: v(Linear velocity) = rω v=2πr/T ω (angular velocity)=2πf f (frequency)= 1/T (time period) T= 2πr/v a (centripetal acceleration)=v^2/r F (centripetal force)=mv^2/r So now.. my attempt: r= v/ω = √ar/2πf = (√(a*(vT/2π))/2πf 2πfr=√(a*(vT/2π) 2πfr^2= a * (vT/2π) 2π * 2πfr^2 = a * vT ...... I'm lost I have so many variables that I need to eliminate and I'm not sure what else to do from here. Help would be very appreciated.
 Sci Advisor PF Gold P: 11,888 Hi I am not sure what you are trying to do. Radius and frequency are entirely different quantities and they are not directly related except when you state the situation that you are studying. You have written down some equations that relate them and some other quantities. What are you trying to achieve by jiggling around the original equations in the second half? I think you are trying for something that is impossible or has no meaning. Could you explain more fully, please?
P: 3
 Quote by sophiecentaur Hi I am not sure what you are trying to do. Radius and frequency are entirely different quantities and they are not directly related except when you state the situation that you are studying. You have written down some equations that relate them and some other quantities. What are you trying to achieve by jiggling around the original equations in the second half? I think you are trying for something that is impossible or has no meaning. Could you explain more fully, please?
okay, so the whole situation from what I've been told by my teacher is that we are deriving an equation for the radius in terms of frequency for a "rotor machine" aka the type of amusement rides that spin so fast that people are pushed against the walls and can't move. That is all the info that we've really been given for the equation. My teacher says this is a simple derivation but it seems very complicated to me. :(

 Emeritus Sci Advisor HW Helper Thanks PF Gold P: 6,271 Derivation of r (radius) in terms of f (frequency)? Help please. Well, which of the equations you listed in the OP would be useful in figuring out how a person can be pushed up against the outer wall of the ride as it turns? What is keeping the person pressed up against the wall?