The Units of Displacement in CGS and FPS Systems

Displacement is a fundamental measurement in physics, particularly in hydrodynamics. The units of displacement can be expressed in two historically significant measurement systems: the CGS (Centimetre-Gram-Second) and FPS (Foot-Pound-Second) systems. Understanding these units is crucial for comprehending the principles of fluid dynamics and mechanics. This article delves into the specific units of displacement within these systems and their historical context.

Linear Displacement in CGS and FPS Systems

When discussing linear displacement, the CGS and FPS systems use distinctly different units. In the CGS system, linear displacement is measured in centimetres (cm). This system is named after the three fundamental units: centimetres for length, grams for mass, and seconds for time. Similarly, in the FPS system, linear displacement is measured in feet (ft). The FPS system took a different approach, focusing on feet for length and the pound for mass, with the same second for time.

Displacement of Volumes in CGS and FPS Systems

The measurement of the displacement of a volume of liquid, such as that displaced by a ship, is more complex. Here, both the CGS and FPS systems use the cubic unit to measure the volume of liquid displaced. Specifically, in the CGS system, the displacement of a volume of liquid is measured in cubic centimetres (cm3). This unit is derived from the fundamental unit of length, the centimetre, for all three dimensions. In the FPS system, the measurement is in cubic feet (ft3), which is the cubic unit derived from the foot.

A Historical Perspective on Measurement Systems

While these units have been crucial in their time, it is important to recognize their historical context. The CGS system, although still used in some scientific literature, is now considered outdated. The adoption of the International System of Units (SI) in the 20th century has largely superseded the CGS system. The FPS system is similarly dated and has mostly been replaced by the MKS (Metre-Kilogram-Second) and MKSA (MKS with Ampere) systems.

Resources for Further Study

A comprehensive review of the CGS and FPS systems can be found in the following references:

Elert, Glenn. (2019a). “British-American System of Units – The Physics Hypertextbook.” In The Physics Hypertextbook Online. Brooklyn: Glenn Elert. Elert, Glenn. (2019b). “Gaussian System of Units – The Physics Hypertextbook.” In The Physics Hypertextbook Online. Brooklyn: Glenn Elert.

These resources provide a detailed exploration of how these systems were historically used and why they have largely been replaced by more modern and universally accepted systems of measurement.

Conclusion

The units of displacement in the CGS and FPS systems offer a glimpse into the evolution of physical measurement systems. While the CGS and FPS units of displacement (centimetres and feet for linear displacement, and cubic centimetres and cubic feet for volume displacement) are still relevant in certain contexts, the shift to more modern and internationally recognized units underscores the importance of adapting to changing scientific standards.