Which of the following is a characteristic of dynamic forces?

Dynamic forces are fundamentally associated with motion. When an object is in motion, it experiences forces that can change its state of movement or the shape of the object itself. This relationship is essential in understanding how structures and materials respond under varying conditions.

For instance, when vehicles travel on a road, the dynamic forces come into play due to acceleration, deceleration, and turning movements. These forces can affect not only the moving objects but also the surfaces they interact with, requiring careful consideration in design and analysis during surveying.

The other choices do not accurately describe dynamic forces. Forces acting on stationary objects pertain to static forces, while consistency regardless of speed is more characteristic of static situations, not dynamic ones where forces can vary with changes in speed. Lastly, dynamic forces are not limited to solid materials; they can also affect fluids and gases, making the last option not applicable. Thus, the correct answer emphasizes that dynamic forces arise from motion, which is the essence of their definition and significance in surveying and engineering design.