## Main Question or Discussion Point

Hey Guys,

I having trouble with understanding radius of gyration, could someone please explain what it is? I have just never understood it's full meaning. So for example, the radius of gyration of a spinning wheel of a car is ....some value... What does that mean?

Thanks

Related General Engineering News on Phys.org
PhanthomJay
For an area, A, with an area moment of inertia of I, the radius of gyration, r, is $r = \sqrt {I/A}$.
For a mass, m, with a mass moment of inertia of I, the radius of gyration, k, is $k = \sqrt{I/m}$.
In either case, it represents the distance of an equivalent line area or point mass , respectively, to the axis about which the moment of inertia is taken, to yield an equivalent moment of inertia. For example, a thin rod of length L has a mass moment of inertia about an axis perpendicular to one end of mL2/3. It's radius of gyration is thus $L/\sqrt 3$, which implies that a point mass located a distance $L/\sqrt 3$ from the end has the same moment of inertia (I = mr2 = mL2/3).