Main Page | See live article | Alphabetical index In special relativity, four-acceleration is a four-vector. The four-acceleration of the four-vector a is defined as the change in four-velocity over the particle's own time: The scalar product of a four-velocity and the corresponding four-acceleration is always 0. See also: four-vector, four-velocity, four-momentum, four-force. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.