- Am I right in saying that accelerations can only be given a sign if a coordinate system is defined in relation to which they are described?
- Is this idea applied to any vector quantity?
- Is there a guideline for this?
1 Answer
More or less.
Velocity, accelerations are vector quantities. You can get a scalar quantity related to a direction taking the dot product of the vector quantity $\mathbf{v}$ of interest and a unit-length vector $\mathbf{\hat{t}}$ in the desired direction,
$$v_t = \mathbf{v} \cdot \mathbf{\hat{t}} \ .$$
If you introduce a base, or a set of coordinates inducing a base, you could perform (be careful with non-Cartesian coordinates) projection of the vector over the vectors of this base.