Negative and positive accelerations are dynamic, mechanical stresses which occur in two main types during the transportation of goods:
- regular acceleration forces and
- irregular acceleration forces.

Regular acceleration forces primarily occur in maritime transport. Acceleration of up to one g (g = 9.81 [m/s²]) and, in extreme cases, even more, may occur due to rolling and pitching in rough seas. Such regular acceleration forces have an impact on the effort involved in load securing.

Irregular acceleration forces occur during cornering or when a train passes over switches, during braking, starting up, hoisting and lowering. Such acceleration forces are not generally repeated, but they may occur several times at varying intensities during transport. These are the typical stresses of land transport and transport, handling and storage operations.