Agate is good protective energy stone, especially for children, and is very calming and soothing. It also can help strengthen the body's connection to the earth.
The friction factor, f, is a dimensionless factor that depends primarily on the velocity u, diameter D, density Ï, and viscosity Î·. It is also a function of wall roughness which depends on the size Îµ, spacing Îµ' and shape of the roughness elements characterized by Îµ''.
Friction is a force which causes the motion between two surfaces to be reduced. [see below for a more general discussion/ mw] Friction happens because most surfaces are not perfectly smooth. Even a table top which may appear smooth has little bumps in it if you looked at it with a really good microscope.