acceleration

The rate of change of velocity. Also a vector. In one dimension, `a = dv/dt = d²x/dt²`; constant acceleration produces velocity that is linear in time and position that is quadratic. Newton's second law `F = ma` says force and acceleration are proportional, with mass as the conversion factor. On Earth's surface, near the ground, the acceleration of any object in free fall is approximately constant — a single number that does not depend on the object's mass.