For a particle moving along a curve C traced by r(t), the derivative of r(t) carries a physical interpretation used throughout this module.
Velocity
v(t)=r′(t)
v(t) is tangent to C and points in the direction of motion.
Speed
v(t)=∥v(t)∥=∥r′(t)∥
Acceleration
a(t)=v′(t)=r′′(t)
a(t) measures how the velocity vector changes, both in magnitude (speed) and in direction.