Chemical equilibrium exhibits no change on the macroscopic level. A first class lever in a condition of static equilibrium remains at rest. The sum of all of the moments of the forces acting is zero. A gradient is a description of a pattern or variation. The description includes both the magnitude and the direction of the change.
Light intensity decreases in a predictable manner as the distance from the light source increases.
On a mountain, the direction in which the change of slope is smallest is the most desirable route to build a railroad line. It is an action within one system which causes a similar action within another system. It is the belief that certain differences exceed those that would be expected to be caused by chance alone. Validation is a belief that similar relationships obtained by two or more different methods reflect an accurate representation of the situation being investigated. Carbon-14 dating can be used to check the authenticity of archaeological artifacts.