Acceleration is change of velocity per time
One metre per second squared means velocity changes by one metre per second during each second. Forms such as km/h/s express the same quantity through a different velocity scale.
A signed value is a component along a chosen axis. Whether an object speeds up depends on both velocity and acceleration directions, not the acceleration sign alone.
Standard gravity is not local gravity
The symbol gₙ denotes the conventional standard acceleration of free fall. It provides a fixed comparison factor; it does not claim that a local gravimeter would read exactly 9.80665 m/s².
| Unit | Definition used | Boundary |
|---|---|---|
| m/s² | SI coherent acceleration unit | Linear acceleration |
| Gal | 0.01 m/s² exactly | Historical non-SI name |
| gₙ | 9.80665 m/s² exactly | Conventional reference, not local measurement |
| km/h/s | Change of km/h each second | Not km/h² |
Force requires mass
Force follows F = ma. Acceleration alone cannot be converted to newtons, pound-force, or weight without mass and a physical model, so force units are excluded.
Velocity, jerk, and angular acceleration remain separate
Velocity requires time and an initial condition. Jerk measures change of acceleration per time. Angular acceleration uses rad/s². None is a fixed synonym for linear acceleration.
Authoritative references: BIPM SI Brochure, NIST SP 811 Appendix B.9, and JCGM VIM3 conventional quantity value.