# Physical meaning of Radius of Gyration

1. Jan 16, 2012

### Chirag740

Out of many properties polymer scientists are interested to calculate one of the most common is "Rg" i.e. Radius of Gyration. Can anyone put more light on the physical significance of this value?

Can Rg value of two polymers be compared? If yes what conclusion can be drawn from such comparison?

2. Jan 19, 2012

### PrakashPhy

For a mass distribution of a rigid body we can calculate the moment of inertia of that mass distribution about any axis (around it- [within it as well]). The moment of inertia differs for the same mass taken through different axes.

Suppose we have calculated the moment of inertia of a mass distribution through an axis. So radius of gyration is such an arbitrary distance from the given axis at which a point mass of the same mass (as the given mass distribution) can be supposed to have stayed so that it would give same moment of inertia as the mass distribution.

So basically radius of gyration is "average" of distances of each point mass in a mass distribution.

[My "average" here is not arithmetic mean or geometric mean ...]